We have a large square grid with H rows and W columns.
Iroha is now standing in the top-left cell.
She will repeat going right or down to the adjacent cell, until she reaches the bottom-right cell.
However, she cannot enter the cells in the intersection of the bottom A rows and the leftmost B columns. (That is, there are A×B forbidden cells.) There is no restriction on entering the other cells.
Find the number of ways she can travel to the bottom-right cell.
Since this number can be extremely large, print the number modulo 10^9+7.

-----Constraints-----
 -  1 ≦ H, W ≦ 100,000
 -  1 ≦ A < H
 -  1 ≦ B < W

-----Input-----
The input is given from Standard Input in the following format:
H W A B

-----Output-----
Print the number of ways she can travel to the bottom-right cell, modulo 10^9+7.

-----Sample Input-----
2 3 1 1

-----Sample Output-----
2

We have a 2×3 grid, but entering the bottom-left cell is forbidden. The number of ways to travel is two: "Right, Right, Down" and "Right, Down, Right".

Difficulty: interview

Starter code:

Solutions:
from operator  import mul
from functools import reduce

def cmb(n, r, p):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n-r] % p

p = 10 ** 9 + 7
N = 10 ** 6
fact    = [1, 1]  # fact[n] = (n! mod p)
factinv = [1, 1]  # factinv[n] = ((n!)^(-1) mod p)
inv     = [0, 1]

for i in range(2, N + 1):
    fact.append((fact[-1] * i) % p)
    inv.append((-inv[p % i] * (p // i)) % p)
    factinv.append((factinv[-1] * inv[-1]) % p)

#kari1 = '2 3 1 1'                   #2
#kari1 = '10 7 3 4'                  #3570
#kari1 = '100000 100000 99999 99999' #1
#kari1 = '100000 100000 44444 55555' #738162020

"""
in1 = kari1.split()
"""
in1 = input().split()

H = int(in1[0])
W = int(in1[1])
A = int(in1[2])
B = int(in1[3])

allCNT = 0
for idx1 in range(W - B):
    beforeCNT = cmb(H - A + B - 1 + idx1, H - A - 1, p)
    afterCNT  = cmb(W + A - B - 2 - idx1, A - 1, p)
    allCNT    = (allCNT + (beforeCNT * afterCNT) % p) % p

print(allCNT)


h, w, a, b = map(int, input().split())

def cmb1(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return g1[n] * g2[r] * g2[n-r] % mod

mod = 10**9+7 #出力の制限
N = 10**6
g1 = [1, 1] # 元テーブル
g2 = [1, 1] #逆元テーブル
inverse = [0, 1] #逆元テーブル計算用テーブル

for i in range( 2, N + 1 ):
    g1.append( ( g1[-1] * i ) % mod )
    inverse.append( ( -inverse[mod % i] * (mod//i) ) % mod )
    g2.append( (g2[-1] * inverse[-1]) % mod )

ans = 0
for i in range(b, w):
    ans += cmb1(i+h-1-a, i, mod)*cmb1(w-1-i+a-1, a-1, mod)
    ans %= mod
print(ans)

H,W,A,B = list(map(int,input().split()))


class Combination:
    """
  O(n)の前計算を1回行うことで，O(1)でnCr mod mを求められる
  n_max = 10**6のとき前処理は約950ms (PyPyなら約340ms, 10**7で約1800ms)
  使用例：
  comb = Combination(1000000)
  print(comb(5, 3))  # 10
  """

    def __init__(self, n_max, mod=10 ** 9 + 7):
        self.mod = mod
        self.modinv = self.make_modinv_list(n_max)
        self.fac, self.facinv = self.make_factorial_list(n_max)

    def __call__(self, n, r):
        return self.fac[n] * self.facinv[r] % self.mod * self.facinv[n - r] % self.mod

    def make_factorial_list(self, n):
        # 階乗のリストと階乗のmod逆元のリストを返す O(n)
        # self.make_modinv_list()が先に実行されている必要がある
        fac = [1]
        facinv = [1]
        for i in range(1, n + 1):
            fac.append(fac[i - 1] * i % self.mod)
            facinv.append(facinv[i - 1] * self.modinv[i] % self.mod)
        return fac, facinv

    def make_modinv_list(self, n):
        # 0からnまでのmod逆元のリストを返す O(n)
        modinv = [0] * (n + 1)
        modinv[1] = 1
        for i in range(2, n + 1):
            modinv[i] = self.mod - self.mod // i * modinv[self.mod % i] % self.mod
        return modinv

comb = Combination(1000000)
MOD = 10**9+7
ans = 0
for i in range(B,W):
    ans += comb(H-A-1+i,i)*comb(A-1+W-1-i,A-1)
    ans %= MOD
    #print(comb(H-A-1+i,i)*comb(A-1+W-1-i,A-1))
print(ans)




H, W, A, B = map(int, open(0).read().split())
MOD = 10**9+7

factorials = [1] * (H + W + 1)
inv_factorials = [1] * (H + W + 1)

for i in range(H + W):
    factorials[i+1] = factorials[i] * (i + 1) % MOD

inv_factorials = list(map(lambda n: pow(n, -1, MOD), factorials))

def modcomb(m, n, mod):
    return factorials[m] * inv_factorials[n] % MOD * inv_factorials[m - n] % MOD
 
total = modcomb(H + W - 2, W - 1, MOD)
 
for i in range(B):
    total -= modcomb(H - A - 1 + i, i, MOD) * modcomb(A - 1 + W - 1 - i, W - 1 - i, MOD) % MOD
    total %= MOD
 
print(total)

H, W, A, B = map(int, input().split())
mod = 10**9+7

F = [1]*200010
p = 1
for i in range(1, len(F)):
  F[i] = p = p*i%mod

def comb(n, k):
  return F[n]*pow(F[n-k], mod-2, mod)*pow(F[k], mod-2, mod)%mod

ans = 0
for h in range(H-A):
  x = comb(B-1+h, h) # 右にB-1回、下にh回移動する方法の数
  y = comb(W+H-B-h-2, H-h-1) # 右にW-B-1回、下にH-h-1回移動する方法の数
  ans += x*y
  ans %= mod
print(ans)

import sys

def comb(n, r, fact, revfact, mod):
    return (fact[n] * revfact[n-r] * revfact[r]) % mod

def solve():
    H, W, A, B = map(int, input().split())
    mod = 7 + 10 ** 9
    fact = [1] * (H + W + 4)
    revfact = [1] * (H + W + 4)
    for i in range(1, H + W + 4): fact[i] = (i * fact[i-1]) % mod
    revfact[H + W + 3] = pow(fact[H + W + 3], mod - 2, mod)
    for i in reversed(range(1, H + W + 3)): revfact[i] = ((i + 1) * revfact[i + 1]) % mod

    ans = 0
    for j in range(B + 1, W + 1):
        up = comb(H - A + j - 2, j - 1, fact, revfact, mod)
        down = comb(A + W - j - 1, A - 1, fact, revfact, mod)
        ans += (up * down) % mod
        ans %= mod
    print(ans)

    return 0

def __starting_point():
    solve()
__starting_point()

import sys
sys.setrecursionlimit(10000000)
MOD = 10 ** 9 + 7
INF = 10 ** 15

def main():
    H,W,A,B = map(int,input().split())
    MAXN = H + W + 3
    factorial = [1]
    for i in range(1,MAXN + 1):
        factorial.append(factorial[-1]*i%MOD)
    inv_factorial = [-1] * (MAXN + 1)
    inv_factorial[-1] = pow(factorial[-1],MOD - 2,MOD)
    for i in range(MAXN - 1,-1,-1):
        inv_factorial[i] = inv_factorial[i + 1]*(i + 1)%MOD
    
    fact = lambda N:factorial[N]
    nck = lambda N,K: 0 if K > N or K < 0 else factorial[N]*inv_factorial[N - K]*inv_factorial[K]%MOD
    dist = lambda sy,sx,gy,gx: nck(gy - sy + gx - sx,gy - sy)
    ans = 0
    if H - A < W - B:
        H,W = W,H
        A,B = B,A
    
    for i in range(W - B):
        x = B + i + 1
        y = H - A - i
        ans += dist(1,1,y,x)*dist(y,x,H,W)%MOD
        ans %= MOD
    print(ans)
def __starting_point():
    main()
__starting_point()

H,W,A,B=map(int,input().split())
MAX_NUM = 2*10**5 + 1
pr = 10**9+7
fac  = [0 for _ in range(MAX_NUM)]
finv = [0 for _ in range(MAX_NUM)]
inv  = [0 for _ in range(MAX_NUM)]
fac[0]  = fac[1] = 1
finv[0] = finv[1] = 1
inv[1] = 1
for i in range(2,MAX_NUM):
    fac[i] = fac[i-1] * i % pr
    inv[i] = pr - inv[pr%i] * (pr // i) % pr
    finv[i] = finv[i-1] * inv[i] % pr
def c(n,k):
    if n < k:
        return 0
    if n < 0 or k < 0:
        return 0
    return fac[n] * (finv[k] * finv[n-k] % pr) % pr
a=0
while 1:
    a=(a+c(H-A-1+B,B)*c(A+W-B-1,A))%pr
    A+=1
    B+=1
    if A==H or B==W:
        break
print(a)

# Combination
MOD = 10**9+7
MAX = 2*10**5
fac = [1,1] + [0]*MAX
finv = [1,1] + [0]*MAX
inv = [0,1] + [0]*MAX
for i in range(2,MAX+2):
    fac[i] = fac[i-1] * i % MOD
    inv[i] = -inv[MOD%i] * (MOD // i) % MOD
    finv[i] = finv[i-1] * inv[i] % MOD

def comb(n,r):
    if n < r: return 0
    if n < 0 or r < 0: return 0
    return fac[n] * (finv[r] * finv[n-r] % MOD) % MOD

H, W, A, B = list(map(int, input().split()))
ans = 0
for i in range(1, H-A+1):
    cnt = comb(i-1+B-1, i-1)
    #print(i, cnt)
    cnt *= comb(H-i+W-B-1, H-i)
    ans += cnt
    ans %= MOD
print(ans)


#!/usr/bin/env python3
import sys
sys.setrecursionlimit(10**8)
INF = float("inf")

MOD = 1000000007  # type: int


class Combination(object):

    def __init__(self, N, mod=MOD):
        fac, finv, inv = [0]*(N+1), [0]*(N+1), [0]*(N+1)
        fac[:2] = 1, 1
        finv[:2] = 1, 1
        inv[1] = 1
        for i in range(2, N+1):
            fac[i] = fac[i-1]*i % mod
            inv[i] = -inv[mod % i]*(mod//i) % mod
            finv[i] = finv[i-1]*inv[i] % mod
        self.N = N
        self.MOD = mod
        self.fac = fac
        self.finv = finv
        self.inv = inv

    def __call__(self, n, k):
        if n < k:
            return 0
        if n < 0 or k < 0:
            return 0
        fac = self.fac
        finv = self.finv
        mod = self.MOD
        return fac[n] * (finv[k]*finv[n-k] % mod) % mod


def solve(H: int, W: int, A: int, B: int):

    cmb = Combination(H+W+1, MOD)

    ans = 0
    for i in range(B, W):
        buf = cmb(H-A-1+i, i)
        buf *= cmb(A+W-i-2, W-i-1)
        buf %= MOD
        ans += buf
        ans %= MOD
    print(ans)

    return


def main():

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    H = int(next(tokens))  # type: int
    W = int(next(tokens))  # type: int
    A = int(next(tokens))  # type: int
    B = int(next(tokens))  # type: int
    solve(H, W, A, B)


def __starting_point():
    main()

__starting_point()

import sys
import numpy as np
from heapq import heappush, heappop 
from bisect import bisect_left as bi_l, bisect_right as bi_r
from collections import deque, Counter, defaultdict
from itertools import combinations, product
import string 
inf = float('inf')
MOD = 10**9+7
# MOD = 998244353


class NumberTheory():
  def __init__(self, n=2*10**6, numpy=True):
    self.n = n
    self.np_flg = numpy 
    self.is_prime_number, self.prime_numbers = self.sieve_of_eratosthenes(n)
  
  def sieve_of_eratosthenes(self, n):
    if self.np_flg:
      sieve = np.ones(n+1, dtype=np.int64); sieve[:2] = 0
      for i in range(2, int(n**.5)+1):
        if sieve[i]: sieve[i*2::i] = 0
      prime_numbers = np.flatnonzero(sieve)
    else:
      sieve = [1] * (n+1); sieve[0] = sieve[1] = 0
      for i in range(2, int(n**.5)+1):
        if not sieve[i]: continue
        for j in range(i*2, n+1, i): sieve[j] = 0
      prime_numbers = [i for i in range(2, n+1) if sieve[i]]
    return sieve, prime_numbers 

  def prime_factorize(self, n):
    res = dict()
    if n < 2: return res
    border = int(n**.5)
    for p in self.prime_numbers:
      if p > border: break
      while n % p == 0: res[p] = res.get(p, 0)+1; n //= p
      if n == 1: return res
    res[n] = 1; return res

  def prime_factorize_factorial(self, n):
    res = dict()
    for i in range(2, n+1):
      for p, c in self.prime_factorize(i).items(): res[p] = res.get(p, 0)+c
    return res
  
  @staticmethod
  def gcd(a, b): return gcd(b, a%b) if b else abs(a)

  @staticmethod
  def lcm(a, b): return abs(a // gcd(a, b) * b)

  @staticmethod
  def find_divisors(n):
    divisors = []
    for i in range(1, int(n**.5)+1):
      if n%i: continue
      divisors.append(i)
      j = n // i
      if j != i: divisors.append(j)
    return divisors
  
  @staticmethod
  def base_convert(n, b):
    if not n: return [0]
    res = []
    while n:
      n, r = divmod(n, b)
      if r < 0: n += 1; r -= b
      res.append(r)
    return res


class UnionFind():
  def __init__(self, n=10**6):
    self.root = list(range(n))
    self.height = [0] * n 
    self.size = [1] * n 
  
  def find_root(self, u):
    if self.root[u] == u: return u
    self.root[u] = self.find_root(self.root[u])
    return self.root[u]
  
  def unite(self, u, v):
    ru = self.find_root(u)
    rv = self.find_root(v)
    if ru == rv: return 
    hu = self.height[ru]
    hv = self.height[rv]
    if hu >= hv:
      self.root[rv] = ru 
      self.size[ru] += self.size[rv]
      self.height[ru] = max(hu, hv+1)
    else:
      self.root[ru] = rv 
      self.size[rv] += self.size[ru]


class Combinatorics():
  def __init__(self, N=10**9, n=10**6, mod=10**9+7, numpy=True):
    self.mod = mod
    self.nCr = dict()
    self.np_flg=numpy
    self.make_mod_tables(N, n)

  sys.setrecursionlimit(10**6)
  def choose(self, n, r, mod=None): # no mod, or mod ≠ prime
    if r > n or r < 0: return 0
    if r == 0: return 1
    if (n, r) in self.nCr: return self.nCr[(n, r)]
    if not mod:
      self.nCr[(n, r)] = (self.choose(n-1, r) + self.choose(n-1, r-1))
    else:
      self.nCr[(n, r)] = (self.choose(n-1, r, mod) + self.choose(n-1, r-1, mod)) % mod
    return self.nCr[(n,r)]
  
  def cumprod(self, a):
    p = self.mod
    l = len(a); sql = int(np.sqrt(l)+1)
    a = np.resize(a, sql**2).reshape(sql, sql)
    for i in range(sql-1): a[:, i+1] *= a[:, i]; a[:, i+1] %= p
    for i in range(sql-1): a[i+1] *= a[i, -1]; a[i+1] %= p
    return np.ravel(a)[:l]

  def make_mod_tables(self, N, n):
    p = self.mod
    if self.np_flg:
      fac = np.arange(n+1); fac[0] = 1; fac = self.cumprod(fac)
      ifac = np.arange(n+1, 0, -1); ifac[0] = pow(int(fac[-1]), p-2, p)
      ifac = self.cumprod(ifac)[n::-1]
      n_choose = np.arange(N+1, N-n, -1); n_choose[0] = 1;
      n_choose[1:] = self.cumprod(n_choose[1:])*ifac[1:n+1]%p
    else:
      fac = [None]*(n+1); fac[0] = 1
      for i in range(n): fac[i+1] = fac[i]*(i+1)%p
      ifac = [None]*(n+1); ifac[n] = pow(fac[n], p-2, p)
      for i in range(n, 0, -1): ifac[i-1] = ifac[i]*i%p
      n_choose = [None] * (n+1); n_choose[0] = 1
      for i in range(n): n_choose[i+1] = n_choose[i]*(N-i)%p
      for i in range(n+1): n_choose[i] = n_choose[i]*ifac[i]%p
    self.fac, self.ifac, self.mod_n_choose = fac, ifac, n_choose
  
  def mod_choose(self, n, r):
    return self.fac[n]*self.ifac[r]%self.mod*self.ifac[n-r]%self.mod


def z_algorithm(s):
  n = len(s)
  a = [0] * n; a[0] = n
  l = r = -1
  for i in range(1, n):
    if r >= i: a[i] = min(a[i-l], r-i)
    while i + a[i] < n and s[i+a[i]] == s[a[i]]: a[i] += 1
    if i+a[i] >= r: l, r = i, i+a[i]
  return a


class ABC001():
  def A():
    h1, h2 = map(int, sys.stdin.read().split())
    print(h1-h2)

  def B(): pass
  def C(): pass 
  def D(): pass 


class ABC002():
  def A():
    x, y = map(int, sys.stdin.readline().split())
    print(max(x, y))

  def B():
    vowels = set('aeiou')
    s = sys.stdin.readline().rstrip() 
    t = ''
    for c in s:
      if c in vowels: continue 
      t += c 
    print(t)

  def C():
    *coords, = map(int, sys.stdin.readline().split())
    def triangle_area(x0, y0, x1, y1, x2, y2):
      x1 -= x0; x2 -= x0; y1 -= y0; y2 -= y0;
      return abs(x1*y2 - x2*y1) / 2
    print(triangle_area(*coords))

  def D():
    n, m = map(int, sys.stdin.readline().split())
    edges = set()
    for _ in range(m):
      x, y = map(int, sys.stdin.readline().split())
      x -= 1; y -= 1
      edges.add((x, y))
    cand = []
    for i in range(1, 1<<n):
      s = [j for j in range(n) if i>>j & 1]
      for x, y in combinations(s, 2):
        if (x, y) not in edges: break
      else:
        cand.append(len(s))
    print(max(cand))


class ABC003():
  def A():
    n = int(sys.stdin.readline().rstrip())
    print((n+1)*5000)

  def B():
    atcoder = set('atcoder')
    s, t = sys.stdin.read().split()
    for i in range(len(s)):
      if s[i] == t[i]: continue
      if s[i] == '@' and t[i] in atcoder: continue 
      if t[i] == '@' and s[i] in atcoder: continue
      print('You will lose')
      return 
    print('You can win')

  def C():
    n, k, *r = map(int, sys.stdin.read().split())
    res = 0
    for x in sorted(r)[-k:]:
      res = (res+x) / 2
    print(res)

  def D(): pass 


class ABC004():
  def A():
    print(int(sys.stdin.readline().rstrip())*2)

  def B():
    c = [sys.stdin.readline().rstrip() for _ in range(4)]
    for l in c[::-1]:
      print(l[::-1])

  def C():
    n = int(sys.stdin.readline().rstrip())
    n %= 30
    res = list(range(1, 7))
    for i in range(n):
      i %= 5
      res[i], res[i+1] = res[i+1], res[i]
    print(''.join(map(str, res)))

  def D(): pass 


class ABC005():
  def A():
    x, y = map(int, sys.stdin.readline().split())
    print(y//x)

  def B():
    n, *t = map(int, sys.stdin.read().split())
    print(min(t))

  def C():
    t = int(sys.stdin.readline().rstrip())
    n = int(sys.stdin.readline().rstrip())
    a = [int(x) for x in sys.stdin.readline().split()]
    m = int(sys.stdin.readline().rstrip())
    b = [int(x) for x in sys.stdin.readline().split()]
    i = 0
    for p in b:
      if i == n: print('no'); return 
      while p-a[i] > t:
        i += 1
        if i == n: print('no'); return 
      if a[i] > p: print('no'); return 
      i += 1
    print('yes')

  def D():
    n = int(sys.stdin.readline().rstrip())
    d = np.array([sys.stdin.readline().split() for _ in range(n)], np.int64)
    s = d.cumsum(axis=0).cumsum(axis=1)
    s = np.pad(s, 1)
    max_del = np.zeros((n+1, n+1), dtype=np.int64)
    for y in range(1, n+1):
      for x in range(1, n+1):
        max_del[y, x] = np.amax(s[y:n+1, x:n+1] - s[0:n-y+1, x:n+1] - s[y:n+1, 0:n-x+1] + s[0:n-y+1, 0:n-x+1])
    res = np.arange(n**2+1)[:, None]
    i = np.arange(1, n+1)
    res = max_del[i, np.minimum(res//i, n)].max(axis=1)
    q = int(sys.stdin.readline().rstrip())
    p = np.array(sys.stdin.read().split(), dtype=np.int64)
    print(*res[p], sep='\n')


class ABC006():
  def A():
    n = sys.stdin.readline().rstrip()
    if '3' in n: print('YES')
    elif int(n)%3 == 0: print('YES')
    else: print('NO')

  def B():
    mod = 10007
    t = [0, 0, 1]
    for _ in range(1001001):
      t.append(t[-1]+t[-2]+t[-3]); t[-1] %= mod
    n = int(sys.stdin.readline().rstrip())
    print(t[n-1])
    
  def C():
    n, m = map(int, sys.stdin.readline().split())
    cnt = [0, 0, 0]
    if m == 1: cnt = [-1, -1, -1]
    else:
      if m & 1: m -= 3; cnt[1] += 1; n -= 1
      cnt[2] = m//2 - n 
      cnt[0] = n - cnt[2]
    if cnt[0]<0 or cnt[1]<0 or cnt[2]<0: print(-1, -1, -1)
    else: print(*cnt, sep=' ')
      
  def D():
    n, *c = map(int, sys.stdin.read().split())
    lis = [inf]*n 
    for x in c: lis[bi_l(lis, x)] = x 
    print(n - bi_l(lis, inf))


class ABC007():
  def A():
    n = int(sys.stdin.readline().rstrip())
    print(n-1)

  def B():
    s = sys.stdin.readline().rstrip()
    if s == 'a': print(-1)
    else: print('a')

  def C():
    r, c = map(int, sys.stdin.readline().split())
    sy, sx = map(int, sys.stdin.readline().split())
    gy, gx = map(int, sys.stdin.readline().split())
    sy -= 1; sx -=1; gy -= 1; gx -= 1
    maze = [sys.stdin.readline().rstrip() for _ in range(r)]
    queue = deque([(sy, sx)])
    dist = np.full((r, c), np.inf); dist[sy, sx] = 0
    while queue:
      y, x = queue.popleft()
      for i, j in [(-1, 0), (1, 0), (0, -1), (0, 1)]:
        i += y; j += x
        if maze[i][j] == '#' or dist[i, j] != np.inf: continue 
        dist[i, j] = dist[y, x] + 1
        queue.append((i, j))
    print(int(dist[gy, gx]))
  
  def D(): pass 


class ABC008():
  def A():
    s, t = map(int, sys.stdin.readline().split())
    print(t-s+1)

  def B():
    n, *s = sys.stdin.read().split()
    res = defaultdict(int)
    for name in s: res[name] += 1
    print(sorted(res.items(), key=lambda x: x[1])[-1][0])

  def C():
    n, *a = map(int, sys.stdin.read().split())
    a = np.array(a)
    c = n - np.count_nonzero(a[:, None]%a, axis=1)
    print(np.sum((c+1)//2/c))
  
  def D(): pass

class ABC009():
  def A():
    n = int(sys.stdin.readline().rstrip())
    print((n+1)//2)

  def B():
    n, *a = map(int, sys.stdin.read().split())
    print(sorted(set(a))[-2])
    
  def C():
    n, k = map(int, sys.stdin.readline().split())
    s = list(sys.stdin.readline().rstrip())
    cost = [1]*n
    r = k
    for i in range(n-1):
      q = []
      for j in range(i+1, n):
        if s[j] < s[i] and cost[i]+cost[j] <= r:
          heappush(q, (s[j], cost[i]+cost[j], -j))
      if not q: continue
      _, c, j = heappop(q); j = -j 
      s[i], s[j] = s[j], s[i]
      r -= c 
      cost[i] = cost[j] = 0
    print(''.join(s))
      
  def D(): pass 


class ABC010():
  def A():
    print(sys.stdin.readline().rstrip()+'pp')
  def B():
    n, *a = map(int, sys.stdin.read().split())
    tot = 0
    for x in a:
      c = 0 
      while x%2==0 or x%3==2:
        x -= 1
        c += 1
      tot += c
    print(tot)

  def C():
    sx, sy, gx, gy, t, v, n, *xy = map(int, sys.stdin.read().split())
    x, y = np.array(xy).reshape(-1, 2).T
    def dist(x1, y1, x2, y2):
      return np.sqrt((x2-x1)**2 + (y2-y1)**2)
    ans = 'YES' if (dist(sx, sy, x, y)+dist(x, y, gx, gy) <= v*t).any() else 'NO'
    print(ans)

  def D(): pass 

class ABC011():
  def A():
    n = int(sys.stdin.readline().rstrip())
    print(n%12+1)

  def B():
    s = sys.stdin.readline().rstrip() 
    print(s[0].upper()+s[1:].lower())

  def C():
    n, *ng = map(int, sys.stdin.read().split())
    ng = set(ng)
    if n in ng: print('NO')
    else:
      r = 100
      while n > 0:
        if r == 0: print('NO'); return
        for i in range(3, 0, -1):
          if (n-i) in ng: continue 
          n -= i
          r -= 1
          break 
        else: print('NO'); return 
      print('YES')

  def D(): pass 


class ABC041():
  def A():
    s, i = sys.stdin.read().split()
    i = int(i)
    print(s[i-1])

  def B():
    a, b, c = map(int, sys.stdin.readline().split())
    ans = a * b % MOD * c % MOD 
    print(ans)

  def C():
    n, *a = map(int, sys.stdin.read().split())
    for i, h in sorted(enumerate(a), key=lambda x: -x[1]):
      print(i+1)

  def D():
    n, m, *xy = map(int, sys.stdin.read().split())
    *xy, = zip(*[iter(xy)]*2)
    edges = [0] * n 
    for x, y in xy:
      x -= 1; y -= 1
      edges[x] |= 1<<y
    comb = [None] * (1<<n); comb[0] = 1
    def count(edges, bit):
      if comb[bit] is not None: return comb[bit]
      comb[bit] = 0
      for i in range(n):
        if (bit>>i) & 1 and not edges[i]:
          nxt_bit = bit & ~(1<<i)
          nxt_edges = edges.copy() 
          for j in range(n):
            nxt_edges[j] &= ~(1<<i)
          cnt = count(nxt_edges, nxt_bit)
          comb[bit] += cnt
      return comb[bit]
    print(count(edges, (1<<n)-1))


class ABC042():
  def A():
    a = [int(x) for x in sys.stdin.readline().split()]
    c = Counter(a)
    print('YES' if c[5]==2 and c[7]==1 else 'NO')

  def B():
    n, l, *s = sys.stdin.read().split()
    print(''.join(sorted(s)))

  def C():
    n, k, *d = sys.stdin.read().split()
    l = len(n)
    ok = sorted(set(string.digits)-set(d))
    cand = [int(''.join(p)) for p in product(ok, repeat=l)] + [int(min(x for x in ok if x > '0')+min(ok)*l)]
    print(cand[bi_l(cand, int(n))])

  def D(): pass 
  h, w, a, b = map(int, sys.stdin.read().split())
  combinatorics = Combinatorics(mod=MOD)
  tot = combinatorics.mod_choose(h+w-2, h-1)
  for i in range(h-a, h):
    tot -= combinatorics.mod_choose(i+b-1, i) * combinatorics.mod_choose(h-i+w-b-2, h-1-i)
    tot %= MOD 
  print(tot)
  








class ABC170():
  def A():
    x = [int(x) for x in sys.stdin.readline().split()]
    for i in range(5):
      if x[i] != i+1:
        print(i+1)
        break

  def B():
    x, y = map(int, sys.stdin.readline().split())
    print('Yes' if 2*x <= y <= 4*x and y%2 == 0 else 'No')
      
  def C():
    x, n, *p = map(int, sys.stdin.read().split())
    a = list(set(range(102)) - set(p))
    a = [(abs(y-x), y) for y in a]
    print(sorted(a)[0][1])

  def D():
    n, *a = map(int, sys.stdin.read().split())
    cand = set(a)
    cnt = 0
    for x, c in sorted(Counter(a).items()):
      cnt += c == 1 and x in cand
      cand -= set(range(x*2, 10**6+1, x))
    print(cnt)

  def E():
    n, q = map(int, sys.stdin.readline().split())
    queue = [] 
    num_kindergarten = 2*10**5
    queue_kindergarten = [[] for _ in range(num_kindergarten)]
    highest_kindergarten = [None] * num_kindergarten
    where = [None] * n
    rate = [None] * n

    def entry(i, k):
      where[i] = k
      while queue_kindergarten[k]:
        r, j = heappop(queue_kindergarten[k])
        if where[j] != k or j == i: continue 
        if rate[i] >= -r:
          highest_kindergarten[k] = rate[i]
          heappush(queue, (rate[i], k, i))
        heappush(queue_kindergarten[k], (r, j))
        break
      else:
        highest_kindergarten[k] = rate[i]
        heappush(queue, (rate[i], k, i))
      heappush(queue_kindergarten[k], (-rate[i], i))

    def transfer(i, k):
      now = where[i]
      while queue_kindergarten[now]:
        r, j = heappop(queue_kindergarten[now])
        if where[j] != now or j == i: continue
        if highest_kindergarten[now] != -r:
          highest_kindergarten[now] = -r
          heappush(queue, (-r, now, j))
        heappush(queue_kindergarten[now], (r, j))
        break
      else:
        highest_kindergarten[now] = None
      entry(i, k)

    def inquire():
      while True:
        r, k, i = heappop(queue)
        if where[i] != k or r != highest_kindergarten[k]: continue 
        heappush(queue, (r, k, i))
        return r

    for i in range(n):
      a, b = map(int, sys.stdin.readline().split())
      rate[i] = a 
      entry(i, b-1)
    for _ in range(q):
      c, d = map(int, sys.stdin.readline().split())
      transfer(c-1, d-1)
      print(inquire())
    
  def F(): pass 


class ABC171():
  def A():
    c = sys.stdin.readline().rstrip()
    print('A' if c < 'a' else 'a')

  def B():
    n, k, *p = map(int, sys.stdin.read().split())
    print(sum(sorted(p)[:k]))

  def C():
    n = int(sys.stdin.readline().rstrip())
    n -= 1
    l = 1
    while True:
      if n < pow(26, l):
        break 
      n -= pow(26, l)
      l += 1
    res = ''.join([chr(ord('a')+d%26) for d in NumberTheory.base_convert(n, 26)][::-1])
    res = 'a'*(l-len(res)) + res
    print(res)

  def D():
    n = int(sys.stdin.readline().rstrip())
    a = [int(x) for x in sys.stdin.readline().split()]
    s = sum(a)
    cnt = Counter(a)
    q = int(sys.stdin.readline().rstrip())
    for _ in range(q):
      b, c = map(int, sys.stdin.readline().split())
      s += (c-b)*cnt[b]
      print(s)
      cnt[c] += cnt[b]; cnt[b] = 0

  def E():
    n, *a = map(int, sys.stdin.read().split())
    s = 0
    for x in a: s ^= x 
    b = map(lambda x: x^s, a)
    print(*b, sep=' ')

  def F(): pass 


class ABC172():
  def A(): pass
  def B(): pass
  def C(): pass 
  def D(): pass 
  def E(): pass 
  def F(): pass 


class ABC173():
  def A():
    n = int(sys.stdin.readline().rstrip())
    charge = (n+999)//1000 * 1000 - n
    print(charge)

  def B():
    n, *s = sys.stdin.read().split() 
    c = Counter(s)
    for v in 'AC, WA, TLE, RE'.split(', '):
      print(f'{v} x {c[v]}')

  def C():
    h, w, k = map(int, sys.stdin.readline().split())
    c = [sys.stdin.readline().rstrip() for _ in range(h)]
    tot = 0
    for i in range(1<<h):
      for j in range(1<<w):
        cnt = 0
        for y in range(h):
          for x in range(w):
            if i>>y & 1 or j>>x & 1:
              continue 
            cnt += c[y][x] ==  '#'
        tot += cnt == k
    print(tot)

  def D():
    n, *a = map(int, sys.stdin.read().split())
    a.sort(reverse=True)
    res = a[0] + sum(a[1:1+(n-2)//2])*2 + a[1+(n-2)//2]*(n & 1)
    print(res)

  def E():
    MOD = 10**9+7
    n, k, *a = map(int, sys.stdin.read().split())
    minus = [x for x in a if x < 0]
    plus = [x for x in a if x > 0]
    if len(plus) + len(minus)//2*2 >= k: # plus 
      *minus, = map(abs, minus)
      minus.sort(reverse=True)
      plus.sort(reverse=True)
      cand = []
      if len(minus)&1: minus = minus[:-1]
      for i in range(0, len(minus)-1, 2):
        cand.append(minus[i]*minus[i+1]%MOD)
      if k & 1:
        res = plus[0]
        plus = plus[1:]
      else:
        res = 1
      if len(plus)&1: plus = plus[:-1]
      for i in range(0, len(plus)-1, 2):
        cand.append(plus[i]*plus[i+1]%MOD)
      cand.sort(reverse=True)
      for x in cand[:k//2]:
        res *= x
        res %= MOD 
      print(res)
    elif 0 in a:
      print(0)
    else:
      cand = sorted(map(abs, a))
      res = 1
      for i in range(k):
        res *= cand[i]
        res %= MOD
      res = MOD - res
      print(res)
      pass
  
  def F(): pass 


def __starting_point():
  ABC042.D()
__starting_point()

h, w, a, b = map(int, input().split())

n = 2 * 10 ** 5
k = 2 * 10 ** 5
mod = 10**9 + 7

modinv_table = [-1] * (k+1)
modinv_table[1] = 1
for i in range(2, k+1):
    modinv_table[i] = (-modinv_table[mod % i] * (mod // i)) % mod

def prepare_binomial_coefficients(n, k):
    for i in range(1,n+1):
        bc_num[i] = i * bc_num[i-1] % mod
    bc_num[0] = 0
    for i in range(1,k+1):
        bc_den[i] = modinv_table[i] * bc_den[i-1] % mod
    return

def binomial_coefficients(n, k):
    if n == 0 and k == 0:
        return 1
    return bc_num[n] * bc_den[k] * bc_den[n-k] % mod

bc_num = [1]*(n+1)
bc_den = [1]*(n+1)
prepare_binomial_coefficients(n, n)

mids = [0]*(w-b)
dis_mid = h - a - 1
for i in range(w-b):
    mids[i] = binomial_coefficients(dis_mid+i+b,i+b)

#print(mids)

mids_down = [0]*(w-b)
dis_mid = a
for i in range(w-b):
    mids_down[i] = binomial_coefficients(dis_mid+w-b-i-1,w-b-i-1)

#print(mids_down)

for i in range(w-b-1):
    mids_down[i] -= mids_down[i+1]

#print(mids_down)

for i in range(w-b):
    mids[i] = (mids[i] * mids_down[i]) % mod

#print(mids)

print(sum(mids)%mod)


# -*- coding: UTF-8 -*-

import sys


def get_ints():
    return list(map(int, sys.stdin.readline().strip().split()))


def mul(x, y, mod):
    x %= mod
    y %= mod
    return x * y % mod


def div(x, y, mod):
    x %= mod
    y %= mod
    return x * mod_pow(y, mod - 2, mod) % mod


def mod_pow(a, p, mod):
    if p == 0:
        return 1
    if p % 2 == 0:
        root = mod_pow(a, p / 2, mod)
        return root * root % mod
    else:
        return a * mod_pow(a, p - 1, mod) % mod


def pre_factorial_divs(n, mod, factorials):
    factorial_divs = [0] * (n + 1)

    factorial_divs[n] = div(1, factorials, mod)
    for i in reversed(list(range(n))):
        factorial_divs[i] = mul(factorial_divs[i+1], i+1, mod)
    return factorial_divs


def pre_factorials(n, mod):
    factorials = [0] * (n + 1)
    factorials[0] = 1
    for i in range(n):
        factorials[i + 1] = (i + 1) * factorials[i] % mod
    return factorials


def fast_fast_fermat_comb(a, b, mod, factorials, factorial_divs):
    if len(factorials) == 0:
        raise
    af = factorials[a]
    bf = factorial_divs[b]
    abf = factorial_divs[a - b]
    return mul(mul(af, bf, mod), abf, mod)


def main():
    h, w, a, b = get_ints()

    ans = 0
    mod = 10 ** 9 + 7

    factorials = pre_factorials(h+w-2, mod)
    factorial_divs = pre_factorial_divs(h+w-2, mod, factorials[h+w-2])

    for i in range(h-a):
        x = fast_fast_fermat_comb(b-1+i, b-1, mod, factorials, factorial_divs)
        y = fast_fast_fermat_comb(h+w-3-(b-1+i), w-b-1, mod, factorials, factorial_divs)
        ans += x * y % mod
        ans %= mod

    print(ans)


def __starting_point():
    main()

__starting_point()

H, W, A, B = list(map(int,input().split()))
mod = 10**9+7
C = [1,1]
inv = [0,1]
Cinv = [1,1]
for i in range(2,H+W+1):
    C.append((C[-1]*i)%mod)
    inv.append((-inv[mod%i]*(mod//i)%mod))
    Cinv.append(Cinv[-1]*inv[-1]%mod)
ans = 0
for i in range(H-A):
    a = (C[i+B-1]*C[H-1-i+W-B-1])%mod
    a = (a*Cinv[B-1])%mod
    a = (a*Cinv[i])%mod
    a = (a*Cinv[W-B-1])%mod
    a = (a*Cinv[H-i-1])%mod
    ans += a
    ans %= mod
print(ans)


def ext_euclid(a, b):
    # return (x, y, gcd(a, b)) such that a * x + b * y = gcd(a, b)
    if b == 0:
        return 1, 0, a
    y, x, v = ext_euclid(b, a % b)
    y -= (a // b) * x
    return x, y, v


def mod_inv(a, mod):
    x, _, _ = ext_euclid(a, mod)
    return x % mod


def comb_list_1(H, W, A, B, mod, modinv_list):
    # (h+B-1)_C_(B-1)  (h in {0, ..., H-A-1})
    ret = [0 for _ in range(H - A)]
    c = 1
    for h in range(H - A):
        ret[h] = c
        c *= h + B
        c *= modinv_list[h + 1]
        c %= mod
    return ret


def comb_list_2(H, W, A, B, mod, modinv_list):
    # (-h+H+W-B-2)_C_(W-B-1)  (h in {0, ..., H-A-1})
    ret = [0 for _ in range(H - A)]
    # initial value -> (A+W-B-1)_C_(W-B-1)  (h = H-A-1)
    c = 1
    for a in range(1, A + 1):
        c *= (a + W - B - 1)
        c *= modinv_list[a]
        c %= mod
    # fill elements of result list from the back
    for h in range(H - A - 1, -1, -1):
        ret[h] = c
        c *= H - h + W - B - 1
        c *= modinv_list[H - h]
        c %= mod
    return ret


def main():
    MOD = 10 ** 9 + 7
    H, W, A, B = list(map(int, input().split(' ')))
    modinv_list = [None] + [mod_inv(h, MOD) for h in range(1, H + 1)]  # modinv doesn't exist on h = 0
    combs_1 = comb_list_1(H, W, A, B, MOD, modinv_list)
    combs_2 = comb_list_2(H, W, A, B, MOD, modinv_list)
    ans = 0
    for c1, c2 in zip(combs_1, combs_2):
        ans += c1 * c2
        ans %= MOD
    print(ans)


def __starting_point():
    main()
__starting_point()

import sys

def comb(n, r, mod=None):
    if r == 0 or r == n:
        return 1
    r = min([r, n-r])
    x, y = 1, 1
    ans = 1
    for i in range(1, r+1):
        if mod:
            x *= n+1-i
            y *= i
            x %= mod
            y %= mod
        else:
            ans *= n+1-i
            ans //= i
    ans = x*pow(y, mod-2, mod)%mod if mod else ans
    return ans

def main():
    input = sys.stdin.readline
    h, w, a, b = map(int, input().split())
    mod = pow(10, 9)+7
    
    bef, aft = 1, comb(h+w-b-2, h-1, mod)
    ans = 0
    for i in range(h-a):
        ans += bef*aft
        ans %= mod
        
        bef = bef*(i+b)*pow(i+1, mod-2, mod)%mod
        aft = aft*(h-i-1)*pow(h-i+w-b-2, mod-2, mod)%mod
        
    print(ans)

def __starting_point():
    main()
__starting_point()

mod = 10 ** 9 + 7
h, w, a, b = map(int, input().split())
def comb(n, r):
    if n < r:return 0
    if n < 0 or r < 0:return 0
    return fa[n] * fi[r] % mod * fi[n - r] % mod
fa = [1] * (h + w + 1)
fi = [1] * (h + w + 1)
for i in range(1, h + w + 1):
    fa[i] = fa[i - 1] * i % mod
    fi[i] = pow(fa[i], mod - 2, mod)
ans = 0
for i in range(h - a):
    ans += comb(b + i - 1, b - 1) * comb(h + w - b - i - 2, w - b - 1)
    ans %= mod
print(ans % mod)

class Factorial:
    def __init__(self, n, mod=10**9+7):
        self.fac = [0] * (n+1)
        self.ifac = [0] * (n+1)
        self.fac[0] = 1
        self.ifac[0] = 1
        self.mod = mod
        modmod = self.mod - 2
        for i in range(n):
            self.fac[i+1] = self.fac[i] * (i+1) % self.mod
            self.ifac[i+1] = self.ifac[i] * pow(i+1, modmod, self.mod) % self.mod

    def comb(self, n, r):
        if n == 0 and r == 0:
            return 1
        if n < r or n < 0:
            return 0
        tmp =  self.ifac[n-r] * self.ifac[r] % self.mod
        return tmp * self.fac[n] % self.mod

    def perm(self, n, r):
        if n == 0 and r == 0:
            return 1
        if n < r or n < 0:
            return 0
        return (self.fac[n] * self.ifac[n-r]) % self.mod

h,w,a,b = list(map(int, input().split()))
mod = 10**9+7
fact = Factorial(h+w+1)
ans = 0
c,d = h-a, w-b
for i in range(b+1, w+1):
    d = w-i+1
#     print(i,i+c-2, c-1, fact.comb(i+c-2, c-1),  fact.comb(a+d-2, a-1))
    ans = (ans + fact.comb(i+c-2, c-1) * fact.comb(a+d-2, a-1)) % mod

print(ans)


H, W, A, B = map(int, input().split())
mod = int(1e9) + 7
def inved(a):
  x, y, u, v, k, l = 1, 0, 0, 1, a, mod
  while l != 0:
    x, y, u, v = u, v, x - u * (k // l), y - v * (k // l)
    k, l = l, k % l
  return x % mod
fact = [1 for _ in range(H+W+A+B+1)]
invf = [1 for _ in range(H+W+A+B+1)]
for i in range(H+W+A+B):
  fact[i+1] = (fact[i] * (i + 1)) % mod
invf[-1] = inved(fact[-1])
for i in range(H+W+A+B, 0, -1):
  invf[i-1] = (invf[i] * i) % mod
S = 0
for i in range(H-A):
  S += (fact[i+B-1] * invf[i] * fact[H-i+W-B-2] * invf[H-1-i]) % mod
  S %= mod
S *= (invf[B-1] * invf[W-B-1]) % mod
S %= mod

print(S)

MOD=10**9+7
UPPERLIMIT=2*(10**5)+1
MODMUL=[1, 1]+[0]*(UPPERLIMIT-1)
for i in range(2, UPPERLIMIT+1):
  MODMUL[i]=MODMUL[i-1]*i%MOD
MODDIV=[1]*UPPERLIMIT+[pow(MODMUL[-1], MOD-2, MOD)]
for i in range(UPPERLIMIT, 0, -1):
  MODDIV[i-1]=MODDIV[i]*i%MOD

H, W, A, B=map(int, input().split())

ans=(((MODMUL[H+W-2]*MODDIV[H-1])%MOD)*MODDIV[W-1])%MOD

x=[MODMUL[H-A+B+i-1]*MODDIV[B-1]*MODDIV[H-A+i]%MOD for i in range(A)]
y=[MODMUL[W+A-B-i-1]*MODDIV[W-B]*MODDIV[A-i-1]%MOD for i in range(A)]
for i in range(A-1, 0, -1):
  x[i]-=x[i-1]

for i in range(A):
  ans-=(x[i]*y[i]%MOD)
  ans%=MOD
  
print(ans)

import math
import time

DIV_VALUE = 10**9 + 7

def calcModOfPow(a, n, p):
    btm = a
    ans = 1
    while n != 0:
        # print('btm: {}'.format(btm))
        if n & 1:
            ans = (ans * btm) % p
            # print('ans: {}'.format(ans))
        n = n>>1
        btm = (btm**2) % p
        # print(n)

    return ans

def calcModOfInv(a, p):
    b = p
    x = 1
    y = 0
    while b:
        div = a // b
        a -= div * b
        [a, b] = [b, a]
        x -= div * y
        [x, y] = [y, x]
    
    x %= p
    if x < 0:
        x += p

    return x

class FirstHalf:
    def __init__(self, H, W, A, B):
        self.H = H
        self.W = W
        self.A = A
        self.B = B
        self.k = 0
        self.div = 0
        self.sup = 0
        self.numOfCases = 1

    def getNumOfCases(self):
        if self.k != 0:
            self.numOfCases = self.numOfCases * (
                (self.B + self.k - 1)
            ) * (
                calcModOfInv(self.k, DIV_VALUE)
            ) % DIV_VALUE
        self.k += 1
        # print('----- k == {} -----'.format(self.k))
        # print(self.numOfCases)
        # self.numOfCases %= DIV_VALUE
        return self.numOfCases
        # return self.numOfCases % DIV_VALUE

class SecondHalf:
    def __init__(self, H, W, A, B):
        self.H = H
        self.W = W
        self.A = A
        self.B = B
        self.k = 0
        self.div = 0
        self.numOfCases = 1
        totalval = self.H + self.W - self.B - 2
        loopval = self.H - 1 if self.H < self.W - self.B else self.W - self.B - 1
        for top in range(totalval, totalval - loopval, -1):
            self.numOfCases *= top
            self.numOfCases %= DIV_VALUE
        for bottom in range(loopval, 0, -1):
            self.numOfCases *= calcModOfInv(bottom, DIV_VALUE)
            self.numOfCases %= DIV_VALUE

        # self.numOfCases = (
        #     math.factorial(self.H + self.W - self.B - 2)
        # ) // (
        #     math.factorial(self.W - self.B - 1)
        # ) // (
        #     math.factorial(self.H - 1)
        # )

    def getNumOfCases(self):
        if self.k != 0:
            self.numOfCases = self.numOfCases * (
                self.H - self.k
            ) * (
                calcModOfInv(
                    self.H + self.W - self.B - self.k - 1,
                    DIV_VALUE
                )
            ) % DIV_VALUE
        self.k += 1
        # print(self.numOfCases)
        # self.numOfCases %= DIV_VALUE
        return self.numOfCases
        # return self.numOfCases % DIV_VALUE

def __starting_point():
    [H, W, A, B] = [int(ipt) for ipt in input().split()]
    
    start = time.time()
    fstHlf = FirstHalf(H, W, A, B)
    sndHlf = SecondHalf(H, W, A, B)
    totalCases = 0

    mid = time.time()
    # print('mid: {}'.format(mid - start))
    for _ in range(H - A):
        totalCases += (
            fstHlf.getNumOfCases() * sndHlf.getNumOfCases()
        )
        totalCases %= DIV_VALUE

    end = time.time()
    # print('end: {}'.format(end - mid))
    print(totalCases)

    #print('{} {} {} {}'.format(H, W, A, B))
    #print(DIV_VALUE)

    # for i in range(12):
    #     print('inv: {}'.format(calcModOfInv(i+1, 13)))

__starting_point()

import sys

sys.setrecursionlimit(10 ** 7)
input = sys.stdin.readline
f_inf = float('inf')
mod = 10 ** 9 + 7

class CmbMod:
    def __init__(self, n, p):
        """
        二項係数nCr(n個の区別できるものからr個のものを選ぶ組み合わせの数)をpで割った余りを求める
        """
        self.n = n
        self.p = p
        self.fact = [1, 1]
        self.factinv = [1, 1]
        self.inv = [0, 1]

    def cmb_mod(self, n, r):
        """
        二項係数nCr(mod p)をO(r)にて計算。nが大きいがrは小さい時に使用。
        """
        numer, denom = 1, 1
        for i in range(r):
            numer = (numer * (n - i)) % self.p
            denom = (denom * (i + 1)) % self.p
        return (numer * pow(denom, self.p - 2, self.p)) % self.p

    def prep(self):
        """
        二項係数nCr(mod p)をO(1)で求める為の前処理をO(N)にて実行。
        """
        for i in range(2, self.n + 1):
            self.fact.append((self.fact[-1] * i) % self.p)
            self.inv.append((-self.inv[self.p % i] * (self.p // i)) % self.p)
            self.factinv.append((self.factinv[-1] * self.inv[-1]) % self.p)

    def cmb_mod_with_prep(self, n, r):
        """
        二項係数nCr(mod p)をO(1)で求める。事前にprepを実行する事。
        """
        if (r < 0) or (n < r):
            return 0
        r = min(r, n - r)
        return self.fact[n] * self.factinv[r] * self.factinv[n - r] % self.p


def resolve():
    H, W, A, B = list(map(int, input().split()))
    H -= 1
    W -= 1
    cmb = CmbMod(H + W, mod)
    cmb.prep()
    total = cmb.cmb_mod_with_prep(H + W, H)
    for w in range(B):
        tmp = (cmb.cmb_mod_with_prep(H - A + w, w) * cmb.cmb_mod_with_prep(A - 1 + W - w, A - 1)) % mod
        total -= tmp
        total %= mod
    print(total)


def __starting_point():
    resolve()

__starting_point()

def cmb(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return g1[n] * g2[r] * g2[n-r] % mod

mod = 10**9+7
size = 2*10**5
g1 = [1, 1]
g2 = [1, 1]
inverse = [0, 1]

for i in range( 2, size + 1 ):
    g1.append( ( g1[-1] * i ) % mod )
    inverse.append( ( -inverse[mod % i] * (mod//i) ) % mod )
    g2.append( (g2[-1] * inverse[-1]) % mod )

H, W, A, B = map(int,input().split())

ans = 0

for i in range(W-B):
    ans += cmb(H-A-1+(B+i), B+i, mod) * cmb(A-1+W-B-1-i, A-1, mod)
    ans %= mod

print(ans)

#coding: utf-8
import math
import heapq
import bisect
import numpy as np
from collections import Counter, deque
import itertools
#from scipy.misc import comb

MOD = 10**9+7
H,W,A,B = map(int,input().split())

def comb(a,b):
	p = fac[a-b]*fac[b]%MOD
	return fac[a]*pow(p,MOD-2,MOD)%MOD

fac=[1]
for i in range(H+W):
	fac.append(fac[-1]*(i+1)%MOD)

ans=0
for i in range(W-B):
	p = comb(H-A-1+B+i,B+i)*comb(W-B-i-2+A,A-1)
	ans += p%MOD
	ans %= MOD

print(ans)

N=2*10**5+3
mod=10**9+7
fac=[1]*(N+1)
for i in range(1,N+1):
    fac[i]=fac[i-1]*i%mod
inv_fac=[1]*(N+1)
inv_fac[N]=pow(fac[N],mod-2,mod)
for i in range(N-1,0,-1):
    inv_fac[i]=inv_fac[i+1]*(i+1)%mod
def nCr(n,r):
    if n<0 or r<0 or r>n:
        return 0
    return fac[n]*inv_fac[r]%mod*inv_fac[n-r]%mod
h,w,a,b=map(int,input().split())
ans=nCr(h+w-2,h-1)
for i in range(b):
    ans=(ans-nCr(h-a+i-1,i)*nCr(a+w-i-2,a-1))%mod
print(ans)

h,w,a,b=map(int,input().split())
inv=[0]*(2*max(h,w)+1)
fact=[0]*(2*max(h,w)+1)
inv[0]=1;fact[0]=1
mod=10**9+7
for i in range(1,2*max(h,w)+1):
    fact[i]=fact[i-1]*i%mod
inv[-1]=pow(fact[-1],mod-2,mod)
for i in range(2*max(h,w),0,-1):
    inv[i-1]=inv[i]*i%mod
ans=0
for yoko in range(b+1,w+1):
    re=fact[yoko-1+h-1-a]*inv[h-1-a]*inv[yoko-1]%mod
    rr=fact[w-yoko+a-1]*inv[w-yoko]*inv[a-1]%mod
    ans=(ans+re*rr%mod)%mod
print(ans)

h,w,a,b=list(map(int,input().split()))

p=10**9+7
#p=127

def modp_factorial(n):
    s=1
    for x in range(1,h+1):
        s=(s*x) % p
    return s
def modp_prod(lst):
    s=1
    for x in lst:
        s=(s*x)%p
    return s
def inv(n):
    s=1
    q=p-2
    while q>0:
        if q&1:
            s=(s*n) % p
        n=(n*n) % p
        q>>=1
    return s

l=[1]
f=1
for x in range(1,h+w):
    f=(f*x) % p
    l.append(f)
invl=[inv(l[-1])]
for n in range(h+w-1,1,-1):
    invl.append((invl[-1]*n) % p)

invl.append(1)
invl.reverse()


s=0
for x in range(1,h-a+1):
    s=(s+modp_prod([l[x+b-2],invl[x-1],invl[b-1]\
        ,l[w-b+h-x-1],invl[h-x],invl[w-b-1]])) % p
print(s)


import sys
import numpy as np
from heapq import heappush, heappop 
from bisect import bisect_left as bi_l, bisect_right as bi_r
from collections import deque, Counter, defaultdict
from itertools import combinations, product
import string 
inf = float('inf')
MOD = 10**9+7
# MOD = 998244353


class NumberTheory():
  def __init__(self, n=2*10**6, numpy=True):
    self.n = n
    self.np_flg = numpy 
    self.is_prime_number, self.prime_numbers = self.sieve_of_eratosthenes(n)
  
  def sieve_of_eratosthenes(self, n):
    if self.np_flg:
      sieve = np.ones(n+1, dtype=np.int64); sieve[:2] = 0
      for i in range(2, int(n**.5)+1):
        if sieve[i]: sieve[i*2::i] = 0
      prime_numbers = np.flatnonzero(sieve)
    else:
      sieve = [1] * (n+1); sieve[0] = sieve[1] = 0
      for i in range(2, int(n**.5)+1):
        if not sieve[i]: continue
        for j in range(i*2, n+1, i): sieve[j] = 0
      prime_numbers = [i for i in range(2, n+1) if sieve[i]]
    return sieve, prime_numbers 

  def prime_factorize(self, n):
    res = dict()
    if n < 2: return res
    border = int(n**.5)
    for p in self.prime_numbers:
      if p > border: break
      while n % p == 0: res[p] = res.get(p, 0)+1; n //= p
      if n == 1: return res
    res[n] = 1; return res

  def prime_factorize_factorial(self, n):
    res = dict()
    for i in range(2, n+1):
      for p, c in self.prime_factorize(i).items(): res[p] = res.get(p, 0)+c
    return res
  
  @staticmethod
  def gcd(a, b): return gcd(b, a%b) if b else abs(a)

  @staticmethod
  def lcm(a, b): return abs(a // gcd(a, b) * b)

  @staticmethod
  def find_divisors(n):
    divisors = []
    for i in range(1, int(n**.5)+1):
      if n%i: continue
      divisors.append(i)
      j = n // i
      if j != i: divisors.append(j)
    return divisors
  
  @staticmethod
  def base_convert(n, b):
    if not n: return [0]
    res = []
    while n:
      n, r = divmod(n, b)
      if r < 0: n += 1; r -= b
      res.append(r)
    return res


class UnionFind():
  def __init__(self, n=10**6):
    self.root = list(range(n))
    self.height = [0] * n 
    self.size = [1] * n 
  
  def find_root(self, u):
    if self.root[u] == u: return u
    self.root[u] = self.find_root(self.root[u])
    return self.root[u]
  
  def unite(self, u, v):
    ru = self.find_root(u)
    rv = self.find_root(v)
    if ru == rv: return 
    hu = self.height[ru]
    hv = self.height[rv]
    if hu >= hv:
      self.root[rv] = ru 
      self.size[ru] += self.size[rv]
      self.height[ru] = max(hu, hv+1)
    else:
      self.root[ru] = rv 
      self.size[rv] += self.size[ru]


class Combinatorics():
  def __init__(self, N=10**9, n=10**6, mod=10**9+7, numpy=True):
    self.mod = mod
    self.nCr = dict()
    self.np_flg=numpy
    self.make_mod_tables(N, n)

  sys.setrecursionlimit(10**6)
  def choose(self, n, r, mod=None): # no mod, or mod ≠ prime
    if r > n or r < 0: return 0
    if r == 0: return 1
    if (n, r) in self.nCr: return self.nCr[(n, r)]
    if not mod:
      self.nCr[(n, r)] = (self.choose(n-1, r) + self.choose(n-1, r-1))
    else:
      self.nCr[(n, r)] = (self.choose(n-1, r, mod) + self.choose(n-1, r-1, mod)) % mod
    return self.nCr[(n,r)]
  
  def cumprod(self, a):
    p = self.mod
    l = len(a); sql = int(np.sqrt(l)+1)
    a = np.resize(a, sql**2).reshape(sql, sql)
    for i in range(sql-1): a[:, i+1] *= a[:, i]; a[:, i+1] %= p
    for i in range(sql-1): a[i+1] *= a[i, -1]; a[i+1] %= p
    return np.ravel(a)[:l]

  def make_mod_tables(self, N, n):
    p = self.mod
    if self.np_flg:
      fac = np.arange(n+1); fac[0] = 1; fac = self.cumprod(fac)
      ifac = np.arange(n+1, 0, -1); ifac[0] = pow(int(fac[-1]), p-2, p)
      ifac = self.cumprod(ifac)[n::-1]
      n_choose = np.arange(N+1, N-n, -1); n_choose[0] = 1;
      n_choose[1:] = self.cumprod(n_choose[1:])*ifac[1:n+1]%p
    else:
      fac = [None]*(n+1); fac[0] = 1
      for i in range(n): fac[i+1] = fac[i]*(i+1)%p
      ifac = [None]*(n+1); ifac[n] = pow(fac[n], p-2, p)
      for i in range(n, 0, -1): ifac[i-1] = ifac[i]*i%p
      n_choose = [None] * (n+1); n_choose[0] = 1
      for i in range(n): n_choose[i+1] = n_choose[i]*(N-i)%p
      for i in range(n+1): n_choose[i] = n_choose[i]*ifac[i]%p
    self.fac, self.ifac, self.mod_n_choose = fac, ifac, n_choose
  
  def mod_choose(self, n, r):
    return self.fac[n]*self.ifac[r]%self.mod*self.ifac[n-r]%self.mod


def z_algorithm(s):
  n = len(s)
  a = [0] * n; a[0] = n
  l = r = -1
  for i in range(1, n):
    if r >= i: a[i] = min(a[i-l], r-i)
    while i + a[i] < n and s[i+a[i]] == s[a[i]]: a[i] += 1
    if i+a[i] >= r: l, r = i, i+a[i]
  return a


class ABC001():
  def A():
    h1, h2 = map(int, sys.stdin.read().split())
    print(h1-h2)

  def B(): pass
  def C(): pass 
  def D(): pass 


class ABC002():
  def A():
    x, y = map(int, sys.stdin.readline().split())
    print(max(x, y))

  def B():
    vowels = set('aeiou')
    s = sys.stdin.readline().rstrip() 
    t = ''
    for c in s:
      if c in vowels: continue 
      t += c 
    print(t)

  def C():
    *coords, = map(int, sys.stdin.readline().split())
    def triangle_area(x0, y0, x1, y1, x2, y2):
      x1 -= x0; x2 -= x0; y1 -= y0; y2 -= y0;
      return abs(x1*y2 - x2*y1) / 2
    print(triangle_area(*coords))

  def D():
    n, m = map(int, sys.stdin.readline().split())
    edges = set()
    for _ in range(m):
      x, y = map(int, sys.stdin.readline().split())
      x -= 1; y -= 1
      edges.add((x, y))
    cand = []
    for i in range(1, 1<<n):
      s = [j for j in range(n) if i>>j & 1]
      for x, y in combinations(s, 2):
        if (x, y) not in edges: break
      else:
        cand.append(len(s))
    print(max(cand))


class ABC003():
  def A():
    n = int(sys.stdin.readline().rstrip())
    print((n+1)*5000)

  def B():
    atcoder = set('atcoder')
    s, t = sys.stdin.read().split()
    for i in range(len(s)):
      if s[i] == t[i]: continue
      if s[i] == '@' and t[i] in atcoder: continue 
      if t[i] == '@' and s[i] in atcoder: continue
      print('You will lose')
      return 
    print('You can win')

  def C():
    n, k, *r = map(int, sys.stdin.read().split())
    res = 0
    for x in sorted(r)[-k:]:
      res = (res+x) / 2
    print(res)

  def D(): pass 


class ABC004():
  def A():
    print(int(sys.stdin.readline().rstrip())*2)

  def B():
    c = [sys.stdin.readline().rstrip() for _ in range(4)]
    for l in c[::-1]:
      print(l[::-1])

  def C():
    n = int(sys.stdin.readline().rstrip())
    n %= 30
    res = list(range(1, 7))
    for i in range(n):
      i %= 5
      res[i], res[i+1] = res[i+1], res[i]
    print(''.join(map(str, res)))

  def D(): pass 


class ABC005():
  def A():
    x, y = map(int, sys.stdin.readline().split())
    print(y//x)

  def B():
    n, *t = map(int, sys.stdin.read().split())
    print(min(t))

  def C():
    t = int(sys.stdin.readline().rstrip())
    n = int(sys.stdin.readline().rstrip())
    a = [int(x) for x in sys.stdin.readline().split()]
    m = int(sys.stdin.readline().rstrip())
    b = [int(x) for x in sys.stdin.readline().split()]
    i = 0
    for p in b:
      if i == n: print('no'); return 
      while p-a[i] > t:
        i += 1
        if i == n: print('no'); return 
      if a[i] > p: print('no'); return 
      i += 1
    print('yes')

  def D():
    n = int(sys.stdin.readline().rstrip())
    d = np.array([sys.stdin.readline().split() for _ in range(n)], np.int64)
    s = d.cumsum(axis=0).cumsum(axis=1)
    s = np.pad(s, 1)
    max_del = np.zeros((n+1, n+1), dtype=np.int64)
    for y in range(1, n+1):
      for x in range(1, n+1):
        max_del[y, x] = np.amax(s[y:n+1, x:n+1] - s[0:n-y+1, x:n+1] - s[y:n+1, 0:n-x+1] + s[0:n-y+1, 0:n-x+1])
    res = np.arange(n**2+1)[:, None]
    i = np.arange(1, n+1)
    res = max_del[i, np.minimum(res//i, n)].max(axis=1)
    q = int(sys.stdin.readline().rstrip())
    p = np.array(sys.stdin.read().split(), dtype=np.int64)
    print(*res[p], sep='\n')


class ABC006():
  def A():
    n = sys.stdin.readline().rstrip()
    if '3' in n: print('YES')
    elif int(n)%3 == 0: print('YES')
    else: print('NO')

  def B():
    mod = 10007
    t = [0, 0, 1]
    for _ in range(1001001):
      t.append(t[-1]+t[-2]+t[-3]); t[-1] %= mod
    n = int(sys.stdin.readline().rstrip())
    print(t[n-1])
    
  def C():
    n, m = map(int, sys.stdin.readline().split())
    cnt = [0, 0, 0]
    if m == 1: cnt = [-1, -1, -1]
    else:
      if m & 1: m -= 3; cnt[1] += 1; n -= 1
      cnt[2] = m//2 - n 
      cnt[0] = n - cnt[2]
    if cnt[0]<0 or cnt[1]<0 or cnt[2]<0: print(-1, -1, -1)
    else: print(*cnt, sep=' ')
      
  def D():
    n, *c = map(int, sys.stdin.read().split())
    lis = [inf]*n 
    for x in c: lis[bi_l(lis, x)] = x 
    print(n - bi_l(lis, inf))


class ABC007():
  def A():
    n = int(sys.stdin.readline().rstrip())
    print(n-1)

  def B():
    s = sys.stdin.readline().rstrip()
    if s == 'a': print(-1)
    else: print('a')

  def C():
    r, c = map(int, sys.stdin.readline().split())
    sy, sx = map(int, sys.stdin.readline().split())
    gy, gx = map(int, sys.stdin.readline().split())
    sy -= 1; sx -=1; gy -= 1; gx -= 1
    maze = [sys.stdin.readline().rstrip() for _ in range(r)]
    queue = deque([(sy, sx)])
    dist = np.full((r, c), np.inf); dist[sy, sx] = 0
    while queue:
      y, x = queue.popleft()
      for i, j in [(-1, 0), (1, 0), (0, -1), (0, 1)]:
        i += y; j += x
        if maze[i][j] == '#' or dist[i, j] != np.inf: continue 
        dist[i, j] = dist[y, x] + 1
        queue.append((i, j))
    print(int(dist[gy, gx]))
  
  def D(): pass 


class ABC008():
  def A():
    s, t = map(int, sys.stdin.readline().split())
    print(t-s+1)

  def B():
    n, *s = sys.stdin.read().split()
    res = defaultdict(int)
    for name in s: res[name] += 1
    print(sorted(res.items(), key=lambda x: x[1])[-1][0])

  def C():
    n, *a = map(int, sys.stdin.read().split())
    a = np.array(a)
    c = n - np.count_nonzero(a[:, None]%a, axis=1)
    print(np.sum((c+1)//2/c))
  
  def D(): pass

class ABC009():
  def A():
    n = int(sys.stdin.readline().rstrip())
    print((n+1)//2)

  def B():
    n, *a = map(int, sys.stdin.read().split())
    print(sorted(set(a))[-2])
    
  def C():
    n, k = map(int, sys.stdin.readline().split())
    s = list(sys.stdin.readline().rstrip())
    cost = [1]*n
    r = k
    for i in range(n-1):
      q = []
      for j in range(i+1, n):
        if s[j] < s[i] and cost[i]+cost[j] <= r:
          heappush(q, (s[j], cost[i]+cost[j], -j))
      if not q: continue
      _, c, j = heappop(q); j = -j 
      s[i], s[j] = s[j], s[i]
      r -= c 
      cost[i] = cost[j] = 0
    print(''.join(s))
      
  def D(): pass 


class ABC010():
  def A():
    print(sys.stdin.readline().rstrip()+'pp')
  def B():
    n, *a = map(int, sys.stdin.read().split())
    tot = 0
    for x in a:
      c = 0 
      while x%2==0 or x%3==2:
        x -= 1
        c += 1
      tot += c
    print(tot)

  def C():
    sx, sy, gx, gy, t, v, n, *xy = map(int, sys.stdin.read().split())
    x, y = np.array(xy).reshape(-1, 2).T
    def dist(x1, y1, x2, y2):
      return np.sqrt((x2-x1)**2 + (y2-y1)**2)
    ans = 'YES' if (dist(sx, sy, x, y)+dist(x, y, gx, gy) <= v*t).any() else 'NO'
    print(ans)

  def D(): pass 

class ABC011():
  def A():
    n = int(sys.stdin.readline().rstrip())
    print(n%12+1)

  def B():
    s = sys.stdin.readline().rstrip() 
    print(s[0].upper()+s[1:].lower())

  def C():
    n, *ng = map(int, sys.stdin.read().split())
    ng = set(ng)
    if n in ng: print('NO')
    else:
      r = 100
      while n > 0:
        if r == 0: print('NO'); return
        for i in range(3, 0, -1):
          if (n-i) in ng: continue 
          n -= i
          r -= 1
          break 
        else: print('NO'); return 
      print('YES')

  def D(): pass 


class ABC041():
  def A():
    s, i = sys.stdin.read().split()
    i = int(i)
    print(s[i-1])

  def B():
    a, b, c = map(int, sys.stdin.readline().split())
    ans = a * b % MOD * c % MOD 
    print(ans)

  def C():
    n, *a = map(int, sys.stdin.read().split())
    for i, h in sorted(enumerate(a), key=lambda x: -x[1]):
      print(i+1)

  def D():
    n, m, *xy = map(int, sys.stdin.read().split())
    *xy, = zip(*[iter(xy)]*2)
    edges = [0] * n 
    for x, y in xy:
      x -= 1; y -= 1
      edges[x] |= 1<<y
    comb = [None] * (1<<n); comb[0] = 1
    def count(edges, bit):
      if comb[bit] is not None: return comb[bit]
      comb[bit] = 0
      for i in range(n):
        if (bit>>i) & 1 and not edges[i]:
          nxt_bit = bit & ~(1<<i)
          nxt_edges = edges.copy() 
          for j in range(n):
            nxt_edges[j] &= ~(1<<i)
          cnt = count(nxt_edges, nxt_bit)
          comb[bit] += cnt
      return comb[bit]
    print(count(edges, (1<<n)-1))


class ABC042():
  def A():
    a = [int(x) for x in sys.stdin.readline().split()]
    c = Counter(a)
    print('YES' if c[5]==2 and c[7]==1 else 'NO')

  def B():
    n, l, *s = sys.stdin.read().split()
    print(''.join(sorted(s)))

  def C():
    n, k, *d = sys.stdin.read().split()
    l = len(n)
    ok = sorted(set(string.digits)-set(d))
    cand = [int(''.join(p)) for p in product(ok, repeat=l)] + [int(min(x for x in ok if x > '0')+min(ok)*l)]
    print(cand[bi_l(cand, int(n))])

  def D():
    h, w, a, b = map(int, sys.stdin.read().split())
    combinatorics = Combinatorics(n=2*10**5, mod=MOD, numpy=True)
    tot = combinatorics.mod_choose(h+w-2, h-1)
    i = np.arange(h-a, h)
    ng = np.sum(combinatorics.mod_choose(i+b-1, i) * combinatorics.mod_choose(h-i+w-b-2, h-1-i) % MOD)
    tot -= ng; tot %= MOD
    print(tot)
  

class ABC170():
  def A():
    x = [int(x) for x in sys.stdin.readline().split()]
    for i in range(5):
      if x[i] != i+1:
        print(i+1)
        break

  def B():
    x, y = map(int, sys.stdin.readline().split())
    print('Yes' if 2*x <= y <= 4*x and y%2 == 0 else 'No')
      
  def C():
    x, n, *p = map(int, sys.stdin.read().split())
    a = list(set(range(102)) - set(p))
    a = [(abs(y-x), y) for y in a]
    print(sorted(a)[0][1])

  def D():
    n, *a = map(int, sys.stdin.read().split())
    cand = set(a)
    cnt = 0
    for x, c in sorted(Counter(a).items()):
      cnt += c == 1 and x in cand
      cand -= set(range(x*2, 10**6+1, x))
    print(cnt)

  def E():
    n, q = map(int, sys.stdin.readline().split())
    queue = [] 
    num_kindergarten = 2*10**5
    queue_kindergarten = [[] for _ in range(num_kindergarten)]
    highest_kindergarten = [None] * num_kindergarten
    where = [None] * n
    rate = [None] * n

    def entry(i, k):
      where[i] = k
      while queue_kindergarten[k]:
        r, j = heappop(queue_kindergarten[k])
        if where[j] != k or j == i: continue 
        if rate[i] >= -r:
          highest_kindergarten[k] = rate[i]
          heappush(queue, (rate[i], k, i))
        heappush(queue_kindergarten[k], (r, j))
        break
      else:
        highest_kindergarten[k] = rate[i]
        heappush(queue, (rate[i], k, i))
      heappush(queue_kindergarten[k], (-rate[i], i))

    def transfer(i, k):
      now = where[i]
      while queue_kindergarten[now]:
        r, j = heappop(queue_kindergarten[now])
        if where[j] != now or j == i: continue
        if highest_kindergarten[now] != -r:
          highest_kindergarten[now] = -r
          heappush(queue, (-r, now, j))
        heappush(queue_kindergarten[now], (r, j))
        break
      else:
        highest_kindergarten[now] = None
      entry(i, k)

    def inquire():
      while True:
        r, k, i = heappop(queue)
        if where[i] != k or r != highest_kindergarten[k]: continue 
        heappush(queue, (r, k, i))
        return r

    for i in range(n):
      a, b = map(int, sys.stdin.readline().split())
      rate[i] = a 
      entry(i, b-1)
    for _ in range(q):
      c, d = map(int, sys.stdin.readline().split())
      transfer(c-1, d-1)
      print(inquire())
    
  def F(): pass 


class ABC171():
  def A():
    c = sys.stdin.readline().rstrip()
    print('A' if c < 'a' else 'a')

  def B():
    n, k, *p = map(int, sys.stdin.read().split())
    print(sum(sorted(p)[:k]))

  def C():
    n = int(sys.stdin.readline().rstrip())
    n -= 1
    l = 1
    while True:
      if n < pow(26, l):
        break 
      n -= pow(26, l)
      l += 1
    res = ''.join([chr(ord('a')+d%26) for d in NumberTheory.base_convert(n, 26)][::-1])
    res = 'a'*(l-len(res)) + res
    print(res)

  def D():
    n = int(sys.stdin.readline().rstrip())
    a = [int(x) for x in sys.stdin.readline().split()]
    s = sum(a)
    cnt = Counter(a)
    q = int(sys.stdin.readline().rstrip())
    for _ in range(q):
      b, c = map(int, sys.stdin.readline().split())
      s += (c-b)*cnt[b]
      print(s)
      cnt[c] += cnt[b]; cnt[b] = 0

  def E():
    n, *a = map(int, sys.stdin.read().split())
    s = 0
    for x in a: s ^= x 
    b = map(lambda x: x^s, a)
    print(*b, sep=' ')

  def F(): pass 


class ABC172():
  def A(): pass
  def B(): pass
  def C(): pass 
  def D(): pass 
  def E(): pass 
  def F(): pass 


class ABC173():
  def A():
    n = int(sys.stdin.readline().rstrip())
    charge = (n+999)//1000 * 1000 - n
    print(charge)

  def B():
    n, *s = sys.stdin.read().split() 
    c = Counter(s)
    for v in 'AC, WA, TLE, RE'.split(', '):
      print(f'{v} x {c[v]}')

  def C():
    h, w, k = map(int, sys.stdin.readline().split())
    c = [sys.stdin.readline().rstrip() for _ in range(h)]
    tot = 0
    for i in range(1<<h):
      for j in range(1<<w):
        cnt = 0
        for y in range(h):
          for x in range(w):
            if i>>y & 1 or j>>x & 1:
              continue 
            cnt += c[y][x] ==  '#'
        tot += cnt == k
    print(tot)

  def D():
    n, *a = map(int, sys.stdin.read().split())
    a.sort(reverse=True)
    res = a[0] + sum(a[1:1+(n-2)//2])*2 + a[1+(n-2)//2]*(n & 1)
    print(res)

  def E():
    MOD = 10**9+7
    n, k, *a = map(int, sys.stdin.read().split())
    minus = [x for x in a if x < 0]
    plus = [x for x in a if x > 0]
    if len(plus) + len(minus)//2*2 >= k: # plus 
      *minus, = map(abs, minus)
      minus.sort(reverse=True)
      plus.sort(reverse=True)
      cand = []
      if len(minus)&1: minus = minus[:-1]
      for i in range(0, len(minus)-1, 2):
        cand.append(minus[i]*minus[i+1]%MOD)
      if k & 1:
        res = plus[0]
        plus = plus[1:]
      else:
        res = 1
      if len(plus)&1: plus = plus[:-1]
      for i in range(0, len(plus)-1, 2):
        cand.append(plus[i]*plus[i+1]%MOD)
      cand.sort(reverse=True)
      for x in cand[:k//2]:
        res *= x
        res %= MOD 
      print(res)
    elif 0 in a:
      print(0)
    else:
      cand = sorted(map(abs, a))
      res = 1
      for i in range(k):
        res *= cand[i]
        res %= MOD
      res = MOD - res
      print(res)
      pass
  
  def F(): pass 


def __starting_point():
  ABC042.D()
__starting_point()

P = 10**9+7
fac = [1]
ifac = [1]
ff = 1
for i in range(1,200001):
  ff *= i
  ff %= P
  fac.append(ff)
  ifac.append(pow(ff, P-2, P))
def ncr(n, r): 
  return (fac[n] * ifac[r] % P * ifac[n-r] % P);

h,w,a,b = list(map(int,input().split()))
s = 0
nC = b-1
kC = 0
nD = w-b-1+h-1
kD = h-1
for i in range(h-a):
  C = ncr(nC, kC)
  D = ncr(nD, kD)
  s = (s + C * D) % P
  nC += 1
  kC += 1
  kD -= 1
  nD -= 1
print(s)


class Combination:
    def __init__(self, size, mod=10**9 + 7):
        self.size = size + 2
        self.mod = mod
        self.fact = [1, 1] + [0] * size
        self.factInv = [1, 1] + [0] * size
        self.inv = [0, 1] + [0] * size

        for i in range(2, self.size):
            self.fact[i] = self.fact[i - 1] * i % self.mod
            self.inv[i] = -self.inv[self.mod % i] * (self.mod // i) % self.mod
            self.factInv[i] = self.factInv[i - 1] * self.inv[i] % self.mod

    def npr(self, n, r):
        if n < r or n < 0 or r < 0:
            return 0
        return self.fact[n] * self.factInv[n - r] % self.mod

    def ncr(self, n, r):
        if n < r or n < 0 or r < 0:
            return 0
        return self.fact[n] * (self.factInv[r] * self.factInv[n - r] % self.mod) % self.mod

    def nhr(self, n, r):  # 重複組合せ
        return self.ncr(n + r - 1, n - 1)

    def factN(self, n):
        if n < 0:
            return 0
        return self.fact[n]

H, W, A, B = list(map(int, input().split()))
comb = Combination(H + W + 100)
MOD = 10**9 + 7

ans = 0
for w in range(B + 1, W + 1):
    ans += comb.ncr(H - A + w - 2, w - 1) * comb.ncr(A + W - w - 1, A - 1)
print((ans % MOD))


import sys
import numpy as np
from heapq import heappush, heappop 
from bisect import bisect_left as bi_l, bisect_right as bi_r
from collections import deque, Counter, defaultdict
from itertools import combinations, product
import string 
inf = float('inf')
MOD = 10**9+7
# MOD = 998244353


class NumberTheory():
  def __init__(self, n=2*10**6, numpy=True):
    self.n = n
    self.np_flg = numpy 
    self.is_prime_number, self.prime_numbers = self.sieve_of_eratosthenes(n)
  
  def sieve_of_eratosthenes(self, n):
    if self.np_flg:
      sieve = np.ones(n+1, dtype=np.int64); sieve[:2] = 0
      for i in range(2, int(n**.5)+1):
        if sieve[i]: sieve[i*2::i] = 0
      prime_numbers = np.flatnonzero(sieve)
    else:
      sieve = [1] * (n+1); sieve[0] = sieve[1] = 0
      for i in range(2, int(n**.5)+1):
        if not sieve[i]: continue
        for j in range(i*2, n+1, i): sieve[j] = 0
      prime_numbers = [i for i in range(2, n+1) if sieve[i]]
    return sieve, prime_numbers 

  def prime_factorize(self, n):
    res = dict()
    if n < 2: return res
    border = int(n**.5)
    for p in self.prime_numbers:
      if p > border: break
      while n % p == 0: res[p] = res.get(p, 0)+1; n //= p
      if n == 1: return res
    res[n] = 1; return res

  def prime_factorize_factorial(self, n):
    res = dict()
    for i in range(2, n+1):
      for p, c in self.prime_factorize(i).items(): res[p] = res.get(p, 0)+c
    return res
  
  @staticmethod
  def gcd(a, b): return gcd(b, a%b) if b else abs(a)

  @staticmethod
  def lcm(a, b): return abs(a // gcd(a, b) * b)

  @staticmethod
  def find_divisors(n):
    divisors = []
    for i in range(1, int(n**.5)+1):
      if n%i: continue
      divisors.append(i)
      j = n // i
      if j != i: divisors.append(j)
    return divisors
  
  @staticmethod
  def base_convert(n, b):
    if not n: return [0]
    res = []
    while n:
      n, r = divmod(n, b)
      if r < 0: n += 1; r -= b
      res.append(r)
    return res


class UnionFind():
  def __init__(self, n=10**6):
    self.root = list(range(n))
    self.height = [0] * n 
    self.size = [1] * n 
  
  def find_root(self, u):
    if self.root[u] == u: return u
    self.root[u] = self.find_root(self.root[u])
    return self.root[u]
  
  def unite(self, u, v):
    ru = self.find_root(u)
    rv = self.find_root(v)
    if ru == rv: return 
    hu = self.height[ru]
    hv = self.height[rv]
    if hu >= hv:
      self.root[rv] = ru 
      self.size[ru] += self.size[rv]
      self.height[ru] = max(hu, hv+1)
    else:
      self.root[ru] = rv 
      self.size[rv] += self.size[ru]


class Combinatorics():
  def __init__(self, N=10**9, n=10**6, mod=10**9+7, numpy=True):
    self.mod = mod
    self.nCr = dict()
    self.np_flg=numpy
    self.make_mod_tables(N, n)

  sys.setrecursionlimit(10**6)
  def choose(self, n, r, mod=None): # no mod, or mod ≠ prime
    if r > n or r < 0: return 0
    if r == 0: return 1
    if (n, r) in self.nCr: return self.nCr[(n, r)]
    if not mod:
      self.nCr[(n, r)] = (self.choose(n-1, r) + self.choose(n-1, r-1))
    else:
      self.nCr[(n, r)] = (self.choose(n-1, r, mod) + self.choose(n-1, r-1, mod)) % mod
    return self.nCr[(n,r)]
  
  def cumprod(self, a):
    p = self.mod
    l = len(a); sql = int(np.sqrt(l)+1)
    a = np.resize(a, sql**2).reshape(sql, sql)
    for i in range(sql-1): a[:, i+1] *= a[:, i]; a[:, i+1] %= p
    for i in range(sql-1): a[i+1] *= a[i, -1]; a[i+1] %= p
    return np.ravel(a)[:l]

  def make_mod_tables(self, N, n):
    p = self.mod
    if self.np_flg:
      fac = np.arange(n+1); fac[0] = 1; fac = self.cumprod(fac)
      ifac = np.arange(n+1, 0, -1); ifac[0] = pow(int(fac[-1]), p-2, p)
      ifac = self.cumprod(ifac)[n::-1]
      n_choose = np.arange(N+1, N-n, -1); n_choose[0] = 1;
      n_choose[1:] = self.cumprod(n_choose[1:])*ifac[1:n+1]%p
    else:
      fac = [None]*(n+1); fac[0] = 1
      for i in range(n): fac[i+1] = fac[i]*(i+1)%p
      ifac = [None]*(n+1); ifac[n] = pow(fac[n], p-2, p)
      for i in range(n, 0, -1): ifac[i-1] = ifac[i]*i%p
      n_choose = [None] * (n+1); n_choose[0] = 1
      for i in range(n): n_choose[i+1] = n_choose[i]*(N-i)%p
      for i in range(n+1): n_choose[i] = n_choose[i]*ifac[i]%p
    self.fac, self.ifac, self.mod_n_choose = fac, ifac, n_choose
  
  def mod_choose(self, n, r):
    return self.fac[n]*self.ifac[r]%self.mod*self.ifac[n-r]%self.mod


def z_algorithm(s):
  n = len(s)
  a = [0] * n; a[0] = n
  l = r = -1
  for i in range(1, n):
    if r >= i: a[i] = min(a[i-l], r-i)
    while i + a[i] < n and s[i+a[i]] == s[a[i]]: a[i] += 1
    if i+a[i] >= r: l, r = i, i+a[i]
  return a


class ABC001():
  def A():
    h1, h2 = map(int, sys.stdin.read().split())
    print(h1-h2)

  def B(): pass
  def C(): pass 
  def D(): pass 


class ABC002():
  def A():
    x, y = map(int, sys.stdin.readline().split())
    print(max(x, y))

  def B():
    vowels = set('aeiou')
    s = sys.stdin.readline().rstrip() 
    t = ''
    for c in s:
      if c in vowels: continue 
      t += c 
    print(t)

  def C():
    *coords, = map(int, sys.stdin.readline().split())
    def triangle_area(x0, y0, x1, y1, x2, y2):
      x1 -= x0; x2 -= x0; y1 -= y0; y2 -= y0;
      return abs(x1*y2 - x2*y1) / 2
    print(triangle_area(*coords))

  def D():
    n, m = map(int, sys.stdin.readline().split())
    edges = set()
    for _ in range(m):
      x, y = map(int, sys.stdin.readline().split())
      x -= 1; y -= 1
      edges.add((x, y))
    cand = []
    for i in range(1, 1<<n):
      s = [j for j in range(n) if i>>j & 1]
      for x, y in combinations(s, 2):
        if (x, y) not in edges: break
      else:
        cand.append(len(s))
    print(max(cand))


class ABC003():
  def A():
    n = int(sys.stdin.readline().rstrip())
    print((n+1)*5000)

  def B():
    atcoder = set('atcoder')
    s, t = sys.stdin.read().split()
    for i in range(len(s)):
      if s[i] == t[i]: continue
      if s[i] == '@' and t[i] in atcoder: continue 
      if t[i] == '@' and s[i] in atcoder: continue
      print('You will lose')
      return 
    print('You can win')

  def C():
    n, k, *r = map(int, sys.stdin.read().split())
    res = 0
    for x in sorted(r)[-k:]:
      res = (res+x) / 2
    print(res)

  def D(): pass 


class ABC004():
  def A():
    print(int(sys.stdin.readline().rstrip())*2)

  def B():
    c = [sys.stdin.readline().rstrip() for _ in range(4)]
    for l in c[::-1]:
      print(l[::-1])

  def C():
    n = int(sys.stdin.readline().rstrip())
    n %= 30
    res = list(range(1, 7))
    for i in range(n):
      i %= 5
      res[i], res[i+1] = res[i+1], res[i]
    print(''.join(map(str, res)))

  def D(): pass 


class ABC005():
  def A():
    x, y = map(int, sys.stdin.readline().split())
    print(y//x)

  def B():
    n, *t = map(int, sys.stdin.read().split())
    print(min(t))

  def C():
    t = int(sys.stdin.readline().rstrip())
    n = int(sys.stdin.readline().rstrip())
    a = [int(x) for x in sys.stdin.readline().split()]
    m = int(sys.stdin.readline().rstrip())
    b = [int(x) for x in sys.stdin.readline().split()]
    i = 0
    for p in b:
      if i == n: print('no'); return 
      while p-a[i] > t:
        i += 1
        if i == n: print('no'); return 
      if a[i] > p: print('no'); return 
      i += 1
    print('yes')

  def D():
    n = int(sys.stdin.readline().rstrip())
    d = np.array([sys.stdin.readline().split() for _ in range(n)], np.int64)
    s = d.cumsum(axis=0).cumsum(axis=1)
    s = np.pad(s, 1)
    max_del = np.zeros((n+1, n+1), dtype=np.int64)
    for y in range(1, n+1):
      for x in range(1, n+1):
        max_del[y, x] = np.amax(s[y:n+1, x:n+1] - s[0:n-y+1, x:n+1] - s[y:n+1, 0:n-x+1] + s[0:n-y+1, 0:n-x+1])
    res = np.arange(n**2+1)[:, None]
    i = np.arange(1, n+1)
    res = max_del[i, np.minimum(res//i, n)].max(axis=1)
    q = int(sys.stdin.readline().rstrip())
    p = np.array(sys.stdin.read().split(), dtype=np.int64)
    print(*res[p], sep='\n')


class ABC006():
  def A():
    n = sys.stdin.readline().rstrip()
    if '3' in n: print('YES')
    elif int(n)%3 == 0: print('YES')
    else: print('NO')

  def B():
    mod = 10007
    t = [0, 0, 1]
    for _ in range(1001001):
      t.append(t[-1]+t[-2]+t[-3]); t[-1] %= mod
    n = int(sys.stdin.readline().rstrip())
    print(t[n-1])
    
  def C():
    n, m = map(int, sys.stdin.readline().split())
    cnt = [0, 0, 0]
    if m == 1: cnt = [-1, -1, -1]
    else:
      if m & 1: m -= 3; cnt[1] += 1; n -= 1
      cnt[2] = m//2 - n 
      cnt[0] = n - cnt[2]
    if cnt[0]<0 or cnt[1]<0 or cnt[2]<0: print(-1, -1, -1)
    else: print(*cnt, sep=' ')
      
  def D():
    n, *c = map(int, sys.stdin.read().split())
    lis = [inf]*n 
    for x in c: lis[bi_l(lis, x)] = x 
    print(n - bi_l(lis, inf))


class ABC007():
  def A():
    n = int(sys.stdin.readline().rstrip())
    print(n-1)

  def B():
    s = sys.stdin.readline().rstrip()
    if s == 'a': print(-1)
    else: print('a')

  def C():
    r, c = map(int, sys.stdin.readline().split())
    sy, sx = map(int, sys.stdin.readline().split())
    gy, gx = map(int, sys.stdin.readline().split())
    sy -= 1; sx -=1; gy -= 1; gx -= 1
    maze = [sys.stdin.readline().rstrip() for _ in range(r)]
    queue = deque([(sy, sx)])
    dist = np.full((r, c), np.inf); dist[sy, sx] = 0
    while queue:
      y, x = queue.popleft()
      for i, j in [(-1, 0), (1, 0), (0, -1), (0, 1)]:
        i += y; j += x
        if maze[i][j] == '#' or dist[i, j] != np.inf: continue 
        dist[i, j] = dist[y, x] + 1
        queue.append((i, j))
    print(int(dist[gy, gx]))
  
  def D(): pass 


class ABC008():
  def A():
    s, t = map(int, sys.stdin.readline().split())
    print(t-s+1)

  def B():
    n, *s = sys.stdin.read().split()
    res = defaultdict(int)
    for name in s: res[name] += 1
    print(sorted(res.items(), key=lambda x: x[1])[-1][0])

  def C():
    n, *a = map(int, sys.stdin.read().split())
    a = np.array(a)
    c = n - np.count_nonzero(a[:, None]%a, axis=1)
    print(np.sum((c+1)//2/c))
  
  def D(): pass

class ABC009():
  def A():
    n = int(sys.stdin.readline().rstrip())
    print((n+1)//2)

  def B():
    n, *a = map(int, sys.stdin.read().split())
    print(sorted(set(a))[-2])
    
  def C():
    n, k = map(int, sys.stdin.readline().split())
    s = list(sys.stdin.readline().rstrip())
    cost = [1]*n
    r = k
    for i in range(n-1):
      q = []
      for j in range(i+1, n):
        if s[j] < s[i] and cost[i]+cost[j] <= r:
          heappush(q, (s[j], cost[i]+cost[j], -j))
      if not q: continue
      _, c, j = heappop(q); j = -j 
      s[i], s[j] = s[j], s[i]
      r -= c 
      cost[i] = cost[j] = 0
    print(''.join(s))
      
  def D(): pass 


class ABC010():
  def A():
    print(sys.stdin.readline().rstrip()+'pp')
  def B():
    n, *a = map(int, sys.stdin.read().split())
    tot = 0
    for x in a:
      c = 0 
      while x%2==0 or x%3==2:
        x -= 1
        c += 1
      tot += c
    print(tot)

  def C():
    sx, sy, gx, gy, t, v, n, *xy = map(int, sys.stdin.read().split())
    x, y = np.array(xy).reshape(-1, 2).T
    def dist(x1, y1, x2, y2):
      return np.sqrt((x2-x1)**2 + (y2-y1)**2)
    ans = 'YES' if (dist(sx, sy, x, y)+dist(x, y, gx, gy) <= v*t).any() else 'NO'
    print(ans)

  def D(): pass 

class ABC011():
  def A():
    n = int(sys.stdin.readline().rstrip())
    print(n%12+1)

  def B():
    s = sys.stdin.readline().rstrip() 
    print(s[0].upper()+s[1:].lower())

  def C():
    n, *ng = map(int, sys.stdin.read().split())
    ng = set(ng)
    if n in ng: print('NO')
    else:
      r = 100
      while n > 0:
        if r == 0: print('NO'); return
        for i in range(3, 0, -1):
          if (n-i) in ng: continue 
          n -= i
          r -= 1
          break 
        else: print('NO'); return 
      print('YES')

  def D(): pass 


class ABC041():
  def A():
    s, i = sys.stdin.read().split()
    i = int(i)
    print(s[i-1])

  def B():
    a, b, c = map(int, sys.stdin.readline().split())
    ans = a * b % MOD * c % MOD 
    print(ans)

  def C():
    n, *a = map(int, sys.stdin.read().split())
    for i, h in sorted(enumerate(a), key=lambda x: -x[1]):
      print(i+1)

  def D():
    n, m, *xy = map(int, sys.stdin.read().split())
    *xy, = zip(*[iter(xy)]*2)
    edges = [0] * n 
    for x, y in xy:
      x -= 1; y -= 1
      edges[x] |= 1<<y
    comb = [None] * (1<<n); comb[0] = 1
    def count(edges, bit):
      if comb[bit] is not None: return comb[bit]
      comb[bit] = 0
      for i in range(n):
        if (bit>>i) & 1 and not edges[i]:
          nxt_bit = bit & ~(1<<i)
          nxt_edges = edges.copy() 
          for j in range(n):
            nxt_edges[j] &= ~(1<<i)
          cnt = count(nxt_edges, nxt_bit)
          comb[bit] += cnt
      return comb[bit]
    print(count(edges, (1<<n)-1))


class ABC042():
  def A():
    a = [int(x) for x in sys.stdin.readline().split()]
    c = Counter(a)
    print('YES' if c[5]==2 and c[7]==1 else 'NO')

  def B():
    n, l, *s = sys.stdin.read().split()
    print(''.join(sorted(s)))

  def C():
    n, k, *d = sys.stdin.read().split()
    l = len(n)
    ok = sorted(set(string.digits)-set(d))
    cand = [int(''.join(p)) for p in product(ok, repeat=l)] + [int(min(x for x in ok if x > '0')+min(ok)*l)]
    print(cand[bi_l(cand, int(n))])

  def D():
    h, w, a, b = map(int, sys.stdin.read().split())
    combinatorics = Combinatorics(mod=MOD, numpy=True)
    tot = combinatorics.mod_choose(h+w-2, h-1)
    i = np.arange(h-a, h)
    ng = np.sum(combinatorics.mod_choose(i+b-1, i) * combinatorics.mod_choose(h-i+w-b-2, h-1-i) % MOD)
    tot -= ng; tot %= MOD
    print(tot)
  
  
class ABC170():
  def A():
    x = [int(x) for x in sys.stdin.readline().split()]
    for i in range(5):
      if x[i] != i+1:
        print(i+1)
        break

  def B():
    x, y = map(int, sys.stdin.readline().split())
    print('Yes' if 2*x <= y <= 4*x and y%2 == 0 else 'No')
      
  def C():
    x, n, *p = map(int, sys.stdin.read().split())
    a = list(set(range(102)) - set(p))
    a = [(abs(y-x), y) for y in a]
    print(sorted(a)[0][1])

  def D():
    n, *a = map(int, sys.stdin.read().split())
    cand = set(a)
    cnt = 0
    for x, c in sorted(Counter(a).items()):
      cnt += c == 1 and x in cand
      cand -= set(range(x*2, 10**6+1, x))
    print(cnt)

  def E():
    n, q = map(int, sys.stdin.readline().split())
    queue = [] 
    num_kindergarten = 2*10**5
    queue_kindergarten = [[] for _ in range(num_kindergarten)]
    highest_kindergarten = [None] * num_kindergarten
    where = [None] * n
    rate = [None] * n

    def entry(i, k):
      where[i] = k
      while queue_kindergarten[k]:
        r, j = heappop(queue_kindergarten[k])
        if where[j] != k or j == i: continue 
        if rate[i] >= -r:
          highest_kindergarten[k] = rate[i]
          heappush(queue, (rate[i], k, i))
        heappush(queue_kindergarten[k], (r, j))
        break
      else:
        highest_kindergarten[k] = rate[i]
        heappush(queue, (rate[i], k, i))
      heappush(queue_kindergarten[k], (-rate[i], i))

    def transfer(i, k):
      now = where[i]
      while queue_kindergarten[now]:
        r, j = heappop(queue_kindergarten[now])
        if where[j] != now or j == i: continue
        if highest_kindergarten[now] != -r:
          highest_kindergarten[now] = -r
          heappush(queue, (-r, now, j))
        heappush(queue_kindergarten[now], (r, j))
        break
      else:
        highest_kindergarten[now] = None
      entry(i, k)

    def inquire():
      while True:
        r, k, i = heappop(queue)
        if where[i] != k or r != highest_kindergarten[k]: continue 
        heappush(queue, (r, k, i))
        return r

    for i in range(n):
      a, b = map(int, sys.stdin.readline().split())
      rate[i] = a 
      entry(i, b-1)
    for _ in range(q):
      c, d = map(int, sys.stdin.readline().split())
      transfer(c-1, d-1)
      print(inquire())
    
  def F(): pass 


class ABC171():
  def A():
    c = sys.stdin.readline().rstrip()
    print('A' if c < 'a' else 'a')

  def B():
    n, k, *p = map(int, sys.stdin.read().split())
    print(sum(sorted(p)[:k]))

  def C():
    n = int(sys.stdin.readline().rstrip())
    n -= 1
    l = 1
    while True:
      if n < pow(26, l):
        break 
      n -= pow(26, l)
      l += 1
    res = ''.join([chr(ord('a')+d%26) for d in NumberTheory.base_convert(n, 26)][::-1])
    res = 'a'*(l-len(res)) + res
    print(res)

  def D():
    n = int(sys.stdin.readline().rstrip())
    a = [int(x) for x in sys.stdin.readline().split()]
    s = sum(a)
    cnt = Counter(a)
    q = int(sys.stdin.readline().rstrip())
    for _ in range(q):
      b, c = map(int, sys.stdin.readline().split())
      s += (c-b)*cnt[b]
      print(s)
      cnt[c] += cnt[b]; cnt[b] = 0

  def E():
    n, *a = map(int, sys.stdin.read().split())
    s = 0
    for x in a: s ^= x 
    b = map(lambda x: x^s, a)
    print(*b, sep=' ')

  def F(): pass 


class ABC172():
  def A(): pass
  def B(): pass
  def C(): pass 
  def D(): pass 
  def E(): pass 
  def F(): pass 


class ABC173():
  def A():
    n = int(sys.stdin.readline().rstrip())
    charge = (n+999)//1000 * 1000 - n
    print(charge)

  def B():
    n, *s = sys.stdin.read().split() 
    c = Counter(s)
    for v in 'AC, WA, TLE, RE'.split(', '):
      print(f'{v} x {c[v]}')

  def C():
    h, w, k = map(int, sys.stdin.readline().split())
    c = [sys.stdin.readline().rstrip() for _ in range(h)]
    tot = 0
    for i in range(1<<h):
      for j in range(1<<w):
        cnt = 0
        for y in range(h):
          for x in range(w):
            if i>>y & 1 or j>>x & 1:
              continue 
            cnt += c[y][x] ==  '#'
        tot += cnt == k
    print(tot)

  def D():
    n, *a = map(int, sys.stdin.read().split())
    a.sort(reverse=True)
    res = a[0] + sum(a[1:1+(n-2)//2])*2 + a[1+(n-2)//2]*(n & 1)
    print(res)

  def E():
    MOD = 10**9+7
    n, k, *a = map(int, sys.stdin.read().split())
    minus = [x for x in a if x < 0]
    plus = [x for x in a if x > 0]
    if len(plus) + len(minus)//2*2 >= k: # plus 
      *minus, = map(abs, minus)
      minus.sort(reverse=True)
      plus.sort(reverse=True)
      cand = []
      if len(minus)&1: minus = minus[:-1]
      for i in range(0, len(minus)-1, 2):
        cand.append(minus[i]*minus[i+1]%MOD)
      if k & 1:
        res = plus[0]
        plus = plus[1:]
      else:
        res = 1
      if len(plus)&1: plus = plus[:-1]
      for i in range(0, len(plus)-1, 2):
        cand.append(plus[i]*plus[i+1]%MOD)
      cand.sort(reverse=True)
      for x in cand[:k//2]:
        res *= x
        res %= MOD 
      print(res)
    elif 0 in a:
      print(0)
    else:
      cand = sorted(map(abs, a))
      res = 1
      for i in range(k):
        res *= cand[i]
        res %= MOD
      res = MOD - res
      print(res)
      pass
  
  def F(): pass 


def __starting_point():
  ABC042.D()
__starting_point()

H, W, A, B = list(map(int, input().split()))
mod = 10**9 + 7
U = 2 * 10**5

factorial = [1 for _ in range(U + 1)]
for i in range(1, U + 1):
    factorial[i] = (factorial[i - 1] * i) % mod

inverse = [1 for _ in range(U + 1)]
inverse[U] = pow(factorial[U], mod - 2, mod)
for i in range(U, 0, -1):
    inverse[i - 1] = (inverse[i] * i) % mod


def comb(n, k):
    if k < 0 or k > n:
        return 0
    x = factorial[n]
    x *= inverse[k]
    x %= mod
    x *= inverse[n - k]
    x %= mod
    return x
  
  
ans = 0
for i in range(H - A):
    x = comb(B - 1 + i, i)
    a = H - 1 - i
    b = W - 1 - B
    x *= comb(a + b, a)
    x %= mod
    ans += x
ans %= mod
print(ans)


H, W, A, B = [int(_) for _ in input().split()]
mod = 10 ** 9 + 7
f = [1] * (3 * 10 ** 6 + 10)
for i in range(1, 3 * 10 ** 6 + 10):
    f[i] = i * f[i - 1] % mod
fi = {}


def comb(n, r):
    if r not in fi:
        fi[r] = pow(f[r], mod - 2, mod)
    if n - r not in fi:
        fi[n - r] = pow(f[n - r], mod - 2, mod)
    return (f[n] * fi[r] * fi[n - r]) % mod


ans = 0
for x in range(H - A):
    ans += comb(B - 1 + x, x) * comb(H - x - 2 + W - B, W - B - 1)
    ans %= mod
print(ans)


mod=10**9+7
h,w,a,b=map(int,input().split())
def comb(a,b):
	p=fac[a-b]*fac[b]%mod
	return fac[a]*pow(p,mod-2,mod)%mod
fac=[1]
for i in range(h+w):
	fac.append(fac[-1]*(i+1)%mod)
ans=0
for i in range(w-b):
	p=comb(h-a-1+b+i,b+i)*comb(w-b-i-2+a,a-1)
	ans+=p%mod
	ans%=mod
print(ans)

MODD = 10**9 + 7 

def modinv(a,m)-> int:
    b = m
    u = 1
    v = 0
    while (b):
        t = a // b
        a -= t * b
        a,b= b,a
        u -= t * v
        u,v= v,u
    u %= m
    if (u < 0):
        u += m
    return u


fac=[1]*200001
infac=[1]*200001
aaa=1
for i in range(1,200001):
    aaa=(aaa*i)%MODD
    fac[i]=aaa
    infac[i]=modinv(aaa,MODD)
    #print(fac[i])

import math as m

def perm(x,y,z) -> int:
    #print(fac[x]//(fac[y]*fac[z]))   
    return ((fac[x]*infac[y]*infac[z])%MODD)

h,w,a,b= [int(x) for x in input().split()]
A = h-a
B = b-1
C = h-1
D = w-b-1
j=0
k=B
kl = C
jl = D
ans = 0
for i in range(A):
  ans+=perm(B+i,B,i)*perm(C+D-i,C-i,D)
print(ans%MODD)

h, w, a, b = list(map(int, input().split()))

n = 2 * 10 ** 5
k = 2 * 10 ** 5
mod = 10**9 + 7

modinv_table = [-1] * (k+1)
modinv_table[1] = 1
for i in range(2, k+1):
    modinv_table[i] = (-modinv_table[mod % i] * (mod // i)) % mod

def prepare_binomial_coefficients(n, k):
    for i in range(1,n+1):
        bc_num[i] = i * bc_num[i-1] % mod
    bc_num[0] = 0
    for i in range(1,k+1):
        bc_den[i] = modinv_table[i] * bc_den[i-1] % mod
    return

def binomial_coefficients(n, k):
    if n == 0 and k == 0:
        return 1
    return bc_num[n] * bc_den[k] * bc_den[n-k] % mod

bc_num = [1]*(n+1)
bc_den = [1]*(n+1)
prepare_binomial_coefficients(n, n)

mids = [0]*(w-b)
dis_mid = h - a - 1
for i in range(w-b):
    mids[i] = binomial_coefficients(dis_mid+i+b,i+b)

#print(mids)

mids_down = [0]*(w-b)
dis_mid = a
for i in range(w-b):
    mids_down[i] = binomial_coefficients(dis_mid+w-b-i-1,w-b-i-1)

#print(mids_down)

for i in range(w-b-1):
    mids_down[i] -= mids_down[i+1]

#print(mids_down)

for i in range(w-b):
    mids[i] = (mids[i] * mids_down[i]) % mod

#print(mids)

print((sum(mids)%mod))


#コンビネーション
def cmb(n, r):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n-r] % mod

N = 2 * 10 ** 5 + 1000  # N は必要分だけ用意する
mod = pow(10, 9) + 7
fact = [1, 1]  # fact[n] = (n! mod p)
factinv = [1, 1]  # factinv[n] = ((n!)^(-1) mod p)
inv = [0, 1]  # factinv 計算用

for i in range(2, N + 1):
    fact.append((fact[-1] * i) % mod)
    inv.append((-inv[mod % i] * (mod // i)) % mod)
    factinv.append((factinv[-1] * inv[-1]) % mod)


h, w, a, b = map(int,input().split())
ans = 0
for i in range(h - a):
    ans += (cmb(b - 1 + i, i) * cmb(w - b -  1 + h - i - 1, w - b - 1)) % (10 ** 9 + 7)
print(ans % (10 ** 9 + 7))


# Function to find modulo inverse of b. It returns  
# -1 when inverse doesn't  
# modInverse works for prime m 
def gcd(b, m):
  if b == 0:
    return m
  return gcd(m%b, b)

def modInverse(b,m): 
    g = gcd(b, m) 
    if (g != 1): 
        # print("Inverse doesn't exist")  
        return -1
    else:  
        # If b and m are relatively prime,  
        # then modulo inverse is b^(m-2) mode m  
        return pow(b, m - 2, m) 
  
  
# Function to compute a/b under modulo m  
def modDivide(a,b,m): 
    a = a % m 
    inv = modInverse(b,m) 
    if(inv == -1): 
        print("Division not defined") 
    else: 
        return (inv*a) % m

MOD = (10 ** 9) + 7
H, W, A, B = list(map(int, input().split(' ')))

DP = []
j = 1
for i in range(1,200002):
    j *= i
    j %= MOD
    DP.append(j)

# print(DP)
def factorial(i):
    if (i == 0):
        return 1
    nonlocal DP
    # print(i)
    # print(i, DP[i-1])
    # print(DP[i-1])
    return DP[i-1]

def move2(H, W, A, B):
    numPaths = 0
    h = H-A
    w = W-(W-B)+1
    a = A+1
    pttp = 0
    for b in range(w, W+1):
        # print(h, b, a, W-b+1)
        ttp = (factorial(h+b-2)*modInverse((factorial(h-1)*factorial(b-1))% MOD, MOD)) % MOD
        tpttp = ttp
        ttp -= pttp
        pttp = tpttp
        btp = (factorial(a+(W-b+1)-2)*modInverse((factorial(a-1)*factorial(W-b))% MOD, MOD)) % MOD
        # btp = factorial(a+(W-b+1)-2)//(factorial(a-1)*factorial(W-b))
        numPaths += ttp*btp
    return numPaths

ways = move2(H, W, A, B)
print(ways % (10**9 + 7))

h, w, a, b = map(int, input().split())

MOD = 10 ** 9 + 7
N = h + w + 10
fact = [0 for _ in range(N)]
invfact = [0 for _ in range(N)]
fact[0] = 1
for i in range(1, N):
    fact[i] = fact[i - 1] * i % MOD

invfact[N - 1] = pow(fact[N - 1], MOD - 2, MOD)

for i in range(N - 2, -1, -1):
    invfact[i] = invfact[i + 1] * (i + 1) % MOD
def nCk(n, k):
    if k < 0 or n < k:
        return 0
    else:
        return fact[n] * invfact[k] * invfact[n - k] % MOD
        
ans = 0
a += 1
b += 1
n = h - a + b - 1
n2 = w - b + a - 1
while a <= h and b <= w:
    ans += nCk(n, b - 1) * nCk(n2, w - b)
    ans %= MOD
    a += 1
    b += 1
print(ans)

class nCrMod():
    def __init__(self, mod):
        self.mod = mod
        self.fac = [1, 1]
        self.finv = [1, 1]
        self.inv = [0, 1]

    def prep(self, n):
        mod = self.mod
        f, fi = self.fac[-1], self.finv[-1]
        for i in range(len(self.fac), n + 1):
            fn = f * i % mod
            v = -self.inv[mod % i] * (mod // i) % mod
            fin = fi * v % mod
            f, fi = fn, fin
            self.fac.append(f)
            self.finv.append(fi)
            self.inv.append(v)

    def __call__(self, n, r):
        if len(self.fac) <= n:
            self.prep(n)
        return self.fac[n] * self.finv[r] * self.finv[n - r] % self.mod

def main():
    H, W, A, B = list(map(int, input().split()))
    mod = 10 ** 9 + 7
    nCr = nCrMod(mod)
    r = 0
    a = H - A - 1
    for i in range(B, W):
        r = (r + nCr(a + i, i) * nCr(A - 1 + W - i - 1, W - i - 1)) % mod
    return r


print((main()))


H, W, A, B = list(map(int, input().split()))

MOD = 1000000007

fac = [1, 1]
inverse = [0, 1]
ifac = [1, 1]
  
for i in range(2, H+W):
  fac.append((fac[-1] * i) % MOD)
  inverse.append((-inverse[MOD % i] * (MOD // i))  % MOD)
  ifac.append((ifac[-1] * inverse[i]) % MOD)

def f(n):
  return fac[B+n+H-A-1] * fac[W-B-1-n+A-1] * ifac[B+n] * ifac[H-A-1] * ifac[W-B-1-n] * ifac[A-1]

def sigma(func, frm, to):
  result = 0
  for i in range(frm, to+1):
    result += func(i)
  return result
 
print((sigma(f, 0, W-B-1)%MOD))


def combmod(n, r, p):
    if r < 0 or n < r:
        return 0
    return fact[n] * finv[r] * finv[n-r] % p


p = 10**9+7
N = 10**6
fact = [1, 1]
finv = [1, 1]
inv = [0, 1]

for i in range(2, N+1):
    fact.append((fact[-1] * i) % p)
    inv.append((-inv[p % i] * (p // i)) % p)
    finv.append((finv[-1] * inv[-1]) % p)

h, w, a, b = (int(x) for x in input().split())
ans = 0
for j in range(b, w):
    ans += combmod(h-a-1 + j, j, p) * combmod(a+w-2 - j, w-1 - j, p)
print((ans % p))


# coding:UTF-8
import sys
from math import factorial

MOD = 10 ** 9 + 7

def combInit(n):
    fact = [1]
    finv = [1]
    for i in range(1, n + 1):
        fact.append(fact[i - 1] * i % MOD)
        finv.append(pow(fact[i], MOD - 2, MOD))
    return [fact, finv]

def comb(n, k, f):
    if n < k:
        return 0
    elif n < 0 or k < 0:
        return 0
    else:
        return f[0][n] * (f[1][k] * f[1][n - k] % MOD) % MOD


def perm(n, r):
    return factorial(n) // factorial(r)


def gcb(a, b):
    if b == 0:
        return a
    else:
        return gcb(b, a % b)


def lcm(a, b):
    d = gcb(a, b)
    return int(a / d * b)


def surP(x):
    return x % MOD


def main():
    # ------ 入力 ------#
    h, w, a, b = list(map(int, input().split()))     # スペース区切り連続数字

    # ------ 処理 ------#
    f = combInit(h + w)
    res = 0
    for i in range(b, w):
        res += comb((h-1-a)+i, i, f) * comb((a-1)+(w-1-i), w-1-i, f)

    out = surP(res)
    # ------ 出力 ------#
    print(("{}".format(out)))
    # if flg == 0:
    #     print("YES")
    # else:
    #     print("NO")


def __starting_point():
    main()

__starting_point()

memo=[0]*(10**6+1)
memo[0]=memo[1]=1
mod=10**9+7
for i in range(2,10**6+1):
  memo[i]=(memo[i-1]*i)%mod
def comb(n,k,p):
  return (memo[n]*pow(memo[k],p-2,p)*pow(memo[n-k],p-2,p))%mod
h,w,a,b=map(int,input().split())
ans=0
for i in range(h-a):
  ans+=(comb(b+i-1,i,mod)*comb(h-i-1+w-b-1,w-b-1,mod))%mod
  ans%=mod
print(ans)

# D - いろはちゃんとマス目
def cmb1(n,r,mod):
    if (r<0 or r>n):
        return 0
    r = min(r,n-r)
    return g1[n]*g2[r]*g2[n-r]%mod

h,w,a,b=list(map(int,input().split()))

# 前処理
mod=10**9+7 #出力の制限
n=10**6
g1=[1,1] # 元テーブル
g2=[1,1] # 逆元テーブル
inverse=[0,1] #逆元テーブル計算用テーブル

for i in range(2,n+1):
    g1.append((g1[-1]*i)%mod)
    inverse.append((-inverse[mod%i]*(mod//i))%mod)
    g2.append((g2[-1]*inverse[-1])%mod)

ans = 0
for i in range(b, w):
    ans+=cmb1(i+h-1-a,i,mod)*cmb1(w-1-i+a-1,a-1,mod)
    ans%=mod
print(ans)


h,w,a,b = list(map(int,input().split()))

mod = 10**9+7 
fact = [1,1]
finv = [1,1]
inv = [0,1]
 
for i in range(2,h+w+5):
    fact.append((fact[-1]*i)%mod)
    inv.append((inv[mod%i]*(mod-mod//i))%mod)
    finv.append((finv[-1]*inv[-1])%mod)
 
def nCr(n,r,mod):
    if r > n:
        return 0
    else: 
        return fact[n]*finv[r]*finv[n-r]%mod

ans = 0

for i in range(100000):
    x = h-a-i
    y = b+1+i
    
    if 0 >= x or y > w:
        break
    
    ans += nCr(h+w-x-y,h-x,mod)*nCr(x+y-2,x-1,mod)%mod
    ans %= mod
print(ans)




h,w,a,b = map(int, input().split())
import math
ans = 0
mod = 10**9+7
l =[i for i in range(1,h+w+2)]
for i in range(1,len(l)-1):
    l[i+1] = l[i+1]*l[i]%mod
l = [1]+ l
gyakugen = [pow(l[i], mod-2, mod) for i in range(1, len(l))]
gyakugen = [1] + gyakugen
for p in range(1, w-b+1):
    ans += l[(h-a-1+b+p-1)]*l[w-(b+p)+a-1]*\
    gyakugen[h-a-1]*gyakugen[b+p-1] * gyakugen[a-1]*gyakugen[w-(b+p)]
print(int(ans)%mod)

class ModInt:
    def __init__(self, num, mod):
        self.num = num
        self.mod = mod

    def __str__(self):
        return str(self.num)

    def __repr__(self):
        return "ModInt(num: {}, mod: {}".format(self.num, self.mod)

    def __add__(self, other):
        ret = self.num + other.num
        ret %= self.mod
        return ModInt(ret, self.mod)

    def __sub__(self, other):
        ret = self.num - other.num
        ret %= self.mod
        return ModInt(ret, self.mod)

    def __mul__(self, other):
        ret = self.num * other.num
        ret %= self.mod
        return ModInt(ret, self.mod)

    def pow(self, times):
        pw = pow(self.num, times, self.mod)
        return ModInt(pw, self.mod)

    def inverse(self):
        return self.pow(self.mod - 2)

    def __truediv__(self, other):
        num = self * other.inverse()
        return ModInt(num, self.mod)


h, w, a, b = list(map(int, input().split()))
mod = 10 ** 9 + 7

fact = [ModInt(1, mod)]
inv = [ModInt(1, mod).inverse()] * (h + w - 1)


def comb(n, r):
    return fact[n] * inv[r] * inv[n-r]


for i in range(1, h + w - 1):
    fact.append(fact[-1] * ModInt(i, mod))

inv[h+w-2] = fact[-1].inverse()
for i in range(h + w - 2, 0, -1):
    inv[i-1] = inv[i] * ModInt(i, mod)

ans = ModInt(0, mod)
for hi in range(h - a):
    ans += comb(hi + b - 1, hi) * comb(h - hi - 1 + w - b - 1, w - b - 1)

print(ans)


H,W,A,B = map(int, input().split())

def cmb(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return g1[n] * g2[r] * g2[n-r] % mod

mod = 10**9+7 #出力の制限
g1 = [1, 1] # 元テーブル
g2 = [1, 1] #逆元テーブル
inverse = [0, 1] #逆元テーブル計算用テーブル

for i in range( 2, H+W + 1 ):
    g1.append( ( g1[-1] * i ) % mod )
    inverse.append( ( -inverse[mod % i] * (mod//i) ) % mod )
    g2.append( (g2[-1] * inverse[-1]) % mod )

ans = 0
for h in range(1, H-A+1):
    ans += cmb(h-1+B-1, h-1, mod)*cmb(H-h+W-B-1, H-h, mod)
    ans %= mod

print(ans)

H, W, A, B = [int(_) for _ in input().split()]
mod = 10**9 + 7
 
X = [i for i in range(H + W + 1)]
X[0] = 1
for i in range(2, H + W + 1):
    X[i] = X[i - 1] * i % mod
 
Y = X.copy()
Y[-1] = pow(Y[-1], mod - 2, mod)
for i in range(H + W, 1, -1):
    Y[i - 1] = i * Y[i] % mod
 
 
def comb(x, y):
    return X[x] * Y[y] * Y[x - y] % mod
 
 
ans = 0
for i in range(B, min(B + H - A, W)):
    ans += comb(H - A + B - 1, i) * comb(W + A - B - 1, W - i - 1)
    ans %= mod
print(ans)


import sys, re
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, tan, asin, acos, atan, radians, degrees, log2
from itertools import accumulate, permutations, combinations, combinations_with_replacement, product, groupby
from operator import itemgetter, mul
from copy import deepcopy
from string import ascii_lowercase, ascii_uppercase, digits
from bisect import bisect, bisect_left
from heapq import heappush, heappop
from functools import reduce
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return list(map(int, input().split()))
def LIST(): return list(map(int, input().split()))
def ZIP(n): return list(zip(*(MAP() for _ in range(n))))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7


lim = 2*10**5   #必要そうな階乗の限界を入力

#階乗#
fact = [1] * (lim+1)
for n in range(1, lim+1):
	fact[n] = n * fact[n-1] % mod

#階乗の逆元#
fact_inv = [1]*(lim+1)
fact_inv[lim] = pow(fact[lim], mod-2, mod)
for n in range(lim, 0, -1):
	fact_inv[n-1] = n*fact_inv[n]%mod

def C(n, r):
	return (fact[n]*fact_inv[r]%mod)*fact_inv[n-r]%mod


H, W, A, B = MAP()

ans = 0
for n in range(B, W):
	way = C(H-A-1+n, n)*C(W-n-1+A-1, A-1)%mod
	ans = (ans+way)%mod

print(ans)


h, w, a, b = map(int, input().split())

mod = 10**9 + 7
fac = [1, 1]
inv = [1, 1]
finv = [1, 1]
for i in range(2, h+w+5):
    fac.append(fac[i-1] * i % mod)
    inv.append(mod - inv[mod%i] * (mod//i) % mod)
    finv.append(finv[i-1] * inv[i] % mod)

def nck(n, k):
    if n < k:
        return 0
    if n < 0 or k < 0:
        return 0
    return fac[n] * (finv[k] * finv[n-k] % mod) % mod

ans = 0
for i in range(h-a):
    ans += nck(i+b-1, b-1) * nck(h-1-i + w-b-1, w-b-1) % mod
    ans %= mod

print(ans)

def cmb(n, r, p):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n-r] % p

p = 10 ** 9 + 7
N = 3 * 10 ** 5  # N は必要分だけ用意する
fact = [1, 1]  # fact[n] = (n! mod p)
factinv = [1, 1]  # factinv[n] = ((n!)^(-1) mod p)
inv = [0, 1]  # factinv 計算用
 
for i in range(2, N + 1):
    fact.append((fact[-1] * i) % p)
    inv.append((-inv[p % i] * (p // i)) % p)
    factinv.append((factinv[-1] * inv[-1]) % p)
    
def __starting_point():
  H, W, A, B = list(map(int, input().split()))
  #HW = [[0] * W for i in range(H)]
  p = 10 ** 9 + 7
  #print(HW)
  #visited = [[0] * W for i in range(H)]
  ans = 0
  for i in range(H - A):
    if i == 0:
      ans += cmb(B + i, i, p) * cmb(H + W - B - 2 - i, H - 1 - i, p)
      ans %= p
    else:
      ans += cmb(B + i - 1, i, p) * cmb(H + W - B - 2 - i, H - 1 - i, p)
      ans %= p
  print(ans)
  

__starting_point()

# 練習
import math
h,w,a,b = list(map(int, input().split()))
p = 10**9+7
# 方針
# (0,0)    ~ (0,w-1)
# (h-1,0 )~ (h-1,w-1)で考える
# 通れないのは(h-a) ~ (h-1)行かつ(0) ~ (b-1) 列のところ
# b <= i <= w-1 のiについて1,2,3の組み合わせはそれぞれ以下の通り 
# 1, (0,0) ~ (h-a-1,i)      (h-a-1+i)! /(h-a-1)! * i!
# 2, (h-a-1,i )~(h-a,i)　  1
# 3, (h-a,i) ~ (h-1,w-1)   (a-1+w-1-i)! /(a-1)! * (w-1-i)!
def cmb(n, k, mod, fac, ifac):
    """
    nCkを計算する
    """
    k = min(k, n-k)
    return fac[n] * ifac[k] * ifac[n-k] % mod


def make_tables(mod, n):
    """
    階乗テーブル、逆元の階乗テーブルを作成する
    """
    fac = [1, 1] # 階乗テーブル・・・(1)
    ifac = [1, 1] #逆元の階乗テーブル・・・(2)
    inverse = [0, 1] #逆元テーブル・・・(3)

    for i in range(2, n+1):
        fac.append((fac[-1] * i) % mod)
        inverse.append((-inverse[mod % i] * (mod//i)) % mod)
        ifac.append((ifac[-1] * inverse[-1]) % mod)
    return fac, ifac

fac, ifac = make_tables(p, h+w-2)
total = 0
for i in range(b, w):
    r1 = cmb(h-a-1+i,i,p,fac, ifac)
    r3 = cmb(a-1+w-1-i, a-1,p,fac, ifac)
    
    total = total +( r1*r3)
print(total%p)   

#ライブラリの点検
class Data():
    def __init__(self):
        self.power=1
        self.rev=1     
class Combi():
    def __init__(self,N,mod):
        self.lists=[Data() for _ in range(N+1)]
        self.mod=mod  
        for i in range(2,N+1):
            self.lists[i].power=((self.lists[i-1].power)*i)%self.mod
        self.lists[N].rev=pow(self.lists[N].power,self.mod-2,self.mod)
        for j in range(N,0,-1):
            self.lists[j-1].rev=((self.lists[j].rev)*j)%self.mod

    def combi(self,K,R):
        if K<R:
            return 0
        else:
            return ((self.lists[K].power)*(self.lists[K-R].rev)*(self.lists[R].rev))%self.mod

######################
h,w,a,b=list(map(int,input().split()))
ans=0
mod=10**9+7
C=Combi(w+h+2,mod)
for i in range(h-a):
    ans+=C.combi(b+i-1,i)*C.combi(w+h-2-b-i,h-1-i)%mod
print((ans%mod))
######################


class Calc:
    def __init__(self, max_value, mod):
        """combination(max_value, all)"""
        fact = [-1] * (max_value + 1)
        fact[0] = 1
        fact[1] = 1
        for x in range(2, max_value + 1):
            fact[x] = x * fact[x - 1] % mod

        invs = [1] * (max_value + 1)
        invs[max_value] = pow(fact[max_value], mod - 2, mod)
        for x in range(max_value - 1, 0, -1):
            invs[x] = invs[x + 1] * (x + 1) % mod

        self.fact = fact
        self.invs = invs
        self.mod = mod

    def combination(self, n, r):
        if n - r < r:
            return self.combination(n, n - r)
        if r < 0:
            return 0
        if r == 0:
            return 1
        if r == 1:
            return n
        return self.fact[n] * self.invs[r] * self.invs[n - r] % self.mod


def main():
    MOD = 10 ** 9 + 7
    H, W, A, B = list(map(int, input().split()))

    calc = Calc(max_value=H + W, mod=MOD)

    ans = 0
    for x in range(B, W):
        v = calc.combination(n=(H - A - 1) + x, r=x)
        u = calc.combination(n=(A - 1) + (W - 1 - x), r=A - 1)
        # (H-1)-(H-A)+(W-1)-x
        ans = (ans + v * u) % MOD
    print(ans)


def __starting_point():
    main()

# import sys
#
# sys.setrecursionlimit(10 ** 7)
#
# input = sys.stdin.readline
# rstrip()
# int(input())
# map(int, input().split())

__starting_point()

class Combination:
    """
    SIZEが10^6程度以下の二項係数を何回も呼び出したいときに使う
    使い方:
    comb = Combination(SIZE, MOD)
    comb(10, 3) => 120
    """

    def __init__(self, N, MOD=10 ** 9 + 7):
        self.MOD = MOD
        self.fact, self.inv = self._make_factorial_list(N)

    def __call__(self, n, k):
        if k < 0 or k > n:
            return 0
        res = self.fact[n] * self.inv[k] % self.MOD
        res = res * self.inv[n - k] % self.MOD
        return res

    def _make_factorial_list(self, N):
        fact = [1] * (N + 1)
        inv = [1] * (N + 1)
        MOD = self.MOD
        for i in range(1, N + 1):
            fact[i] = (fact[i - 1] * i) % MOD
        inv[N] = pow(fact[N], MOD - 2, MOD)
        for i in range(N, 0, -1):
            inv[i - 1] = (inv[i] * i) % MOD
        return fact, inv


def __starting_point():
    H, W, A, B = list(map(int, input().split()))
    mod = 10 ** 9 + 7

    comb = Combination(2 * 10 ** 5 + 10, mod)

    ans = 0
    x = H - A
    y = B + 1
    while x > 0 and y <= W:
        path1 = comb(x + y - 2, x - 1)
        path2 = comb(H - x + W - y, H - x)
        ans = (ans + path1*path2) % mod
        x -= 1
        y += 1

    print(ans)

__starting_point()

H, W, A, B = list(map(int, input().split()))

# H行W列 左下から縦A横B

def mod(num):
    return num % (10 ** 9 + 7)
    
n = H + W + 1

fac = [0] * n
rev = [0] * n

fac[0] = 1

for i in range(1, n):
    fac[i] = mod(fac[i-1] * i)


# 逆元の計算 x**(-1) ≡ x**(10**9 + 5) (mod 10**9 + 7)
rev[n-1] = pow(fac[n-1], 10**9 + 5, 10**9 + 7)

for i in range(n - 2, 0, -1):
    rev[i] = mod(rev[i + 1] * (i + 1))

rev[0] = 1

t1 = [0] * (W - B)

for i in range(W - B):
    t1[i] = mod(fac[H - A - 1 + i + B] * mod(rev[B + i] * rev[H - A - 1]))
    
res = 0

for i in range(W - B):
    r = t1[i] * mod(fac[A - 1 + W - B - 1 - i] * mod(rev[A - 1] * rev[W - B - 1 - i]))
    res = mod(res + r)
    
print(res)


LIMIT = 2 * 10 ** 5
fac = [0] * (LIMIT + 10)
fac[0] = 1
inv = [0] * (LIMIT + 10)
MOD = 1_000_000_007
n = 1
for i in range(1, LIMIT + 1):
    n *= i
    n %= MOD
    fac[i] = n
inv[LIMIT] = pow(fac[LIMIT], MOD - 2, MOD)
for i in range(LIMIT, -1, -1):
    inv[i - 1] = (inv[i] * i) % MOD
def C(n, r):
    return (fac[n] * inv[n-r] * inv[r]) % MOD

H, W, A, B = list(map(int, input().split()))
ans = 0
B1 = B - 1
WB1 = W - B - 1
for i in range(H - A):
    ans += C(i + B1, B1) * C(H - i - 1 + WB1, WB1)
    ans %= MOD
print(ans)


M=10**9+7
H,W,A,B = map(int,input().split())
C = 1
ans = 1

for I in range(H-1):
  ans = C = C*(W+H-B-2-I)*pow(I+1,M-2,M)%M

for I in range(1,H-A):
  C = C*(B-1+I)*(H-I)*pow(I*(W+H-B-1-I),M-2,M)%M
  ans+=C

print(ans%M)

H, W, A, B = [int(_) for _ in input().split()]
mod = 10**9 + 7
 
X = [i for i in range(H + W + 1)]
X[0] = 1
for i in range(2, H + W + 1):
    X[i] = X[i - 1] * i % mod
 
Y = X.copy()
Y[-1] = pow(Y[-1], mod - 2, mod)
for i in range(H + W, 1, -1):
    Y[i - 1] = i * Y[i] % mod
 
 
def comb(x, y):
    return X[x] * Y[y] * Y[x - y] % mod
 
 
ans = 0
for i in range(B, min(B + H - A, W)):
    ans += comb(H - A + B - 1, i) * comb(W + A - B - 1, W - i - 1)
    ans %= mod
print(ans)

H, W, A, B = list(map(int, input().split()))
C = H - A
D = W - B
p = 1000000007

def power(a, b): #a^b (mod p)を求める #二分累乗法を使う
    if b == 0:
        return 1
    elif b % 2 == 0:
        return power(a, b//2) ** 2 % p
    else:
        return power(a, b//2) ** 2 * a % p

f = [1] #f[i] = i! % p
for i in range(H+W):
    f.append(f[i] * (i+1) % p)

I_f = [0] * (H+W+1) #I_f[i] = (i!)^(-1) % p
I_f[H+W] = power(f[H+W], p-2)
for i in reversed(list(range(H+W))):
    I_f[i] = I_f[i+1] * (i+1) % p

def combi(a, b): #(a+b)!/a!b! (mod p)を求める
    return f[a+b] * I_f[a] * I_f[b] % p

x = 0
for i in range(C):
    x = (x + combi(i, B-1) * combi(D-1, H-i-1)) % p
print(x)


def main():
    def cmb(n, r, mod):
        if (r < 0 or r > n):
            return 0
        r = min(r, n-r)
        return g1[n] * g2[r] * g2[n-r] % mod

    mod = 10**9+7  # 出力の制限
    N = 10**6
    g1 = [1, 1]  # 元テーブル
    g2 = [1, 1]  # 逆元テーブル
    inverse = [0, 1]  # 逆元テーブル計算用テーブル

    for i in range(2, N + 1):
        g1.append((g1[-1] * i) % mod)
        inverse.append((-inverse[mod % i] * (mod//i)) % mod)
        g2.append((g2[-1] * inverse[-1]) % mod)

    H, W, A, B = list(map(int, input().split()))

    ans = cmb((H+W-2), min(H, W)-1, mod)

    tmp = 0
    for i in range(B):
        t = cmb(H-A-1+i, i, mod)
        t *= cmb(W-1-i + A - 1, A-1, mod)
        tmp += t
        tmp %= mod
    print(((ans - tmp) % mod))


main()


#縦H A

def cmb(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return g1[n] * g2[r] * g2[n-r] % mod

mod = 10**9+7 #出力の制限
N = (10**5)*2
g1 = [1, 1] # 元テーブル
g2 = [1, 1] #逆元テーブル
inverse = [0, 1] #逆元テーブル計算用テーブル

for i in range( 2, N + 1 ):
    g1.append( ( g1[-1] * i ) % mod )
    inverse.append( ( -inverse[mod % i] * (mod//i) ) % mod )
    g2.append( (g2[-1] * inverse[-1]) % mod )
H,W,A,B=list(map(int,input().split()))
ans=0
for i in range(H-A):
  ans+=cmb(B+i-1,B-1,mod) * cmb(H-i+W-B-2,W-B-1,mod)
print((ans%mod))
# 1 1 1
# $ 1 2


class Combination:
    """
    SIZEが10^6程度以下の二項係数を何回も呼び出したいときに使う
    使い方:
    comb = Combination(SIZE, MOD)
    comb(10, 3) => 120
    """

    def __init__(self, N, MOD=10 ** 9 + 7):
        self.MOD = MOD
        self.fact, self.inv = self._make_factorial_list(N)

    def __call__(self, n, k):
        if k < 0 or k > n:
            return 0
        res = self.fact[n] * self.inv[k] % self.MOD
        res = res * self.inv[n - k] % self.MOD
        return res

    def _make_factorial_list(self, N):
        fact = [1] * (N + 1)
        inv = [1] * (N + 1)
        MOD = self.MOD
        for i in range(1, N + 1):
            fact[i] = (fact[i - 1] * i) % MOD
        inv[N] = pow(fact[N], MOD - 2, MOD)
        for i in range(N, 0, -1):
            inv[i - 1] = (inv[i] * i) % MOD
        return fact, inv


def __starting_point():
    H, W, A, B = list(map(int, input().split()))
    mod = 10**9+7
    comb = Combination(2*10**5+10, mod)

    ans = 0
    h1 = H - A
    w1 = B + 1
    while True:
        X = comb(h1 + w1 - 2, h1 - 1)
        h2 = H - h1
        w2 = W - w1
        Y = comb(h2 + w2, h2)
        ans += X * Y % mod
        ans %= mod

        h1 -= 1
        w1 += 1
        if h1 <= 0 or w1 > W:
            break

    print(ans)

__starting_point()

from sys import stdin
input = stdin.readline

MAX = 510000
MOD = 10**9 + 7

def MakeTable():
    fac[0], fac[1] = 1, 1
    finv[0], finv[1] = 1, 1
    inv[1] = 1
    for i in range(2, MAX):
        fac[i] = fac[i - 1] * i % MOD
        inv[i] = MOD - inv[MOD%i] * (MOD // i) % MOD
        finv[i] = finv[i - 1] * inv[i] % MOD

def COM(n, k):
    if n < k:
        return 0
    elif n < 0 or k < 0:
        return 0
    else:
        return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD

H, W, A, B = map(int, input().split())
fac = [0] * MAX
finv = [0] * MAX
inv = [0] * MAX

N = min(H-A, W-B)
x, y = 0, 0
result = 0

MakeTable()

for _ in range(N):
    n1 = H-A-1+B+x-y
    n2 = A+W-1-B-x+y
    result += (COM(n1, B+x) * COM(n2, A+y)) % MOD
    x += 1
    y += 1

print(result%MOD)

h,w,a,b=map(int,input().split())
#コンビネーション逆元
def cmb(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return g1[n] * g2[r] * g2[n-r] % mod


mod = 10**9+7 #出力の制限
N = 10**6
g1 = [1, 1] # 元テーブル
g2 = [1, 1] #逆元テーブル
inverse = [0, 1] #逆元テーブル計算用テーブル


for i in range( 2, N + 1 ):
    g1.append( ( g1[-1] * i ) % mod )
    inverse.append( ( -inverse[mod % i] * (mod//i) ) % mod )
    g2.append( (g2[-1] * inverse[-1]) % mod )
ans=cmb(h+w-2,h-1,mod)
for i in range(h-a+1,h+1):
    ans-=cmb(i+b-2,i-1,mod)*cmb(h-i+w-b-1,w-b-1,mod)
    ans%=mod
print(ans)

h, w, a, b = map(int, input().split())
mod = 10 ** 9 + 7
n = h + w

f = [1 for _ in range(n)]
f_inv = [1 for _ in range(n)]
for i in range(1, n):
    f[i] = f[i-1] * i % mod
    f_inv[i] = pow(f[i], mod-2, mod)


def comb(n, k):
    return (f[n] * f_inv[k] % mod) * f_inv[n-k] % mod

ans = comb(h+w-2, h-1)
for i in range(b):
    ans -= comb(h-a+i-1, i) * comb(a+w-i-2, a-1) % mod
    ans %= mod

print(ans)

mod = 10 ** 9 + 7
N = 10 ** 6
fact = [1, 1]
factinv = [1, 1]
inv = [0, 1]

for i in range(2, N + 1):
    fact.append(fact[-1] * i % mod)
    inv.append((-inv[mod % i] * (mod // i)) % mod)
    factinv.append((factinv[-1] * inv[-1]) % mod)

def combi_mod(n, r, p):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n - r] % p


H, W, A, B = list(map(int, input().split()))

if B < W / 2:
    not_ans = 0
    total = combi_mod((H - 1) + (W - 1), H-1, mod)
    for i in range(B):
        sq1h = H - A
        sq1w = i + 1
        sq2h = A
        sq2w = W - i
        n = combi_mod((sq1h -1) + (sq1w - 1), (sq1h -1), mod) * combi_mod((sq2h - 1) + (sq2w - 1), (sq2h - 1), mod) % mod
        not_ans = (not_ans + n) % mod
    ans = (total - not_ans) % mod
    print(ans)
        
else:
    ans = 0
    for i in range(B, W):
        sq1h = H - A
        sq1w = i + 1
        sq2h = A
        sq2w = W - i
        n = combi_mod((sq1h - 1) + (sq1w - 1), (sq1h - 1), mod) * combi_mod((sq2h - 1) + (sq2w - 1), (sq2h - 1), mod)
        ans = (ans + n) % mod
    ans %= mod
    print(ans)


MOD = 10**9+7

h,w,a,b = map(int,input().split())

n = h+w
fac = [1]*(n+1)
fac_inv =  [0]*(n+1)

for i in range(n):
    fac[i+1] = (fac[i] * (i+1)) %MOD
fac_inv[-1] = pow(fac[-1],MOD-2,MOD)
for i in range(n,0,-1):
    fac_inv[i-1] = (fac_inv[i] * i) % MOD
    
def comb(n,k):
    if k<0 or k>n:
        return 0
    x = (fac[n] * (fac_inv[k] * fac_inv[n-k])%MOD)%MOD
    return x

ans = 0

for i in range(w-b):
    
    ans += comb((h-a-1) + b+i, b+i) * comb((a-1) + (w - b-i-1), a-1) %MOD
    ans %= MOD
    
print(ans)

# -*- coding: utf-8 -*-
#コンビネーション
def cmb(n, r):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n-r] % mod

N = 2 * 10 ** 5 + 1000  # N は必要分だけ用意する
mod = pow(10, 9) + 7
fact = [1, 1]  # fact[n] = (n! mod p)
factinv = [1, 1]  # factinv[n] = ((n!)^(-1) mod p)
inv = [0, 1]  # factinv 計算用

for i in range(2, N + 1):
    fact.append((fact[-1] * i) % mod)
    inv.append((-inv[mod % i] * (mod // i)) % mod)
    factinv.append((factinv[-1] * inv[-1]) % mod)

ans = 0
h, w, a, b = list(map(int,input().split()))
for i in range(h - a):
    #print(b - 1 + i, i, w - b - 1 + h - i - 1, w - b - 1)
    ans += (cmb(b - 1 + i, i) * cmb(w - b -  1 + h - i - 1, w - b - 1)) % (10 ** 9 + 7)
print((ans % (10 ** 9 + 7)))


H, W, A, B = map(int, open(0).read().split())
MOD = 10**9+7

def modcomb(m, n, mod):
    if n > m - n:
        n = m - n
    p = 1
    q = 1
    for i in range(n):
        p = p * (m - i) % mod
        q = q * (i + 1) % mod
    result = p * pow(q, mod - 2, mod) % mod
    return result

total = modcomb(H + W - 2, W - 1, MOD)

tmp = modcomb(A + W - 2, W - 1, MOD)
total -= tmp

for i in range(B - 1):
    a = H - A + i
    b = i + 1
    c = W - i - 1
    d = W + A - 2 - i
#     print(a,b,c,d)
    tmp = tmp * a * c % MOD
    tmp = tmp * pow(b, -1, MOD) % MOD
    tmp = tmp * pow(d, -1, MOD) % MOD
#     print(tmp)
    total = (total - tmp) % MOD

print(total)

def prepare(n, MOD):
    f = 1
    factorials = [1]
    for m in range(1, n + 1):
        f *= m
        f %= MOD
        factorials.append(f)
    inv = pow(f, MOD - 2, MOD)
    invs = [1] * (n + 1)
    invs[n] = inv
    for m in range(n, 1, -1):
        inv *= m
        inv %= MOD
        invs[m - 1] = inv
    return factorials, invs


h, w, a, b = list(map(int, input().split()))
MOD = 10 ** 9 + 7
facts, invs = prepare(h + w, MOD)
ans = 0
ib = invs[b - 1]
iwb = invs[w - b - 1]
for down in range(h - a):
    left_pattern = facts[b - 1 + down] * ib * invs[down] % MOD
    right_pattern = facts[h - 1 - down + w - b - 1] * invs[h - 1 - down] * iwb % MOD
    ans = (ans + left_pattern * right_pattern) % MOD
print(ans)


h, w, a, b = list(map(int, input().split()))
m = 10**9 + 7

fac = [1, 1]
inv = [1, 1]
finv = [1, 1]
for i in range(2, w+h+5):
    fac.append(fac[i-1] * i % m)
    inv.append(m - inv[m%i] * (m//i) % m)
    finv.append(finv[i-1] * inv[i] % m)

def nck(n, k):
    if n < k:
        return 0
    if n < 0 or k < 0:
        return 0
    return fac[n] * (finv[k] * finv[n-k] % m) % m


row = []
for i in range(h-a):
    row.append(nck(b+i, i))

ans = 0
for i in range(len(row)-1):
    ans += row[i] * nck(w-b-2 + h-1-i, h-1-i)
    ans %= m

ans += row[-1] * nck(w-b-1 + a, a)
ans %= m

print(ans)


mod = 10 ** 9 + 7
fact = [1]
inv = [1]
for i in range(200000):
  fact.append(fact[i] * (i + 1) % mod)
  inv.append(pow(fact[i + 1], mod - 2, mod))
def ncr(n, r):
  if n < 0 or r < 0 or n - r < 0:
    return 0
  return fact[n] * inv[r] * inv[n - r] % mod
h, w, a, b = list(map(int, input().split()))
ans = ncr(h + w - 2, h - 1)
for i in range(min(a, b)):
  ans -= ncr(h - a + b - 1, h - a + i) * ncr(w - b + a - 1, w - b + i)
print((ans % mod))


h,w,a,b=list(map(int,input().split()))
fac=[0]*200001#iの階乗mod(1000000007)
inv=[0]*200001#iの逆元mod(1000000007)
fac[0]=1
ans=0
for i in range(1,200001):
    fac[i]=fac[i-1]*i%1000000007
inv[200000]=pow(fac[200000],1000000005,1000000007)
for i in range(199999,0,-1):
    inv[i]=(inv[i+1]*(i+1))%1000000007
    inv[0]=1
for i in range(h-a):
    if i==0:
        if h==1:
            x=1
        else:
            x=(fac[w-b+h-2
                   -i]*inv[w-1-b]*inv[h-1-i])%1000000007
    else:
        x=((fac[b-1+i]*inv[b-1]*inv[i])%1000000007)*((fac[w-b+h-2-i]*inv[w-b-1]*inv[h-1-i])%1000000007)
    ans=(ans+x)%1000000007
print(ans)


import sys, re
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, tan, asin, acos, atan, radians, degrees, log2
from itertools import accumulate, permutations, combinations, combinations_with_replacement, product, groupby
from operator import itemgetter, mul
from copy import deepcopy
from string import ascii_lowercase, ascii_uppercase, digits
from bisect import bisect, bisect_left
from fractions import gcd
from heapq import heappush, heappop
from functools import reduce
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
def ZIP(n): return zip(*(MAP() for _ in range(n)))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7


lim = 2*10**5   #必要そうな階乗の限界を入力

#階乗#
fact = [1] * (lim+1)
for n in range(1, lim+1):
	fact[n] = n * fact[n-1] % mod

#階乗の逆元#
fact_inv = [1]*(lim+1)
fact_inv[lim] = pow(fact[lim], mod-2, mod)
for n in range(lim, 0, -1):
	fact_inv[n-1] = n*fact_inv[n]%mod

def C(n, r):
	return (fact[n]*fact_inv[r]%mod)*fact_inv[n-r]%mod


H, W, A, B = MAP()

ans = 0
for n in range(B, W):
	way = C(H-A-1+n, n)*C(W-n-1+A-1, A-1)%mod
	ans = (ans+way)%mod

print(ans)

class CombinationFermat:

    def __init__(self):
        """O(MAX)で前計算しておく→以降comb(a,b)はO(1)で取得可能
        """
        MOD = 10**9 + 7
        MAX = 2*10**5

        self.fac = [0]*MAX   # self.fac[n]:  (n!) mod p
        self.finv = [0]*MAX  # self.finv[n]: (n!)^-1 mod p
        self.inv = [0]*MAX   # inv[n]:  (n)^-1 mod -p
        self.fac[0] = self.fac[1] = 1
        self.finv[0] = self.finv[1] = 1
        self.inv[1] = 1
        for i in range(2, MAX):
            self.fac[i] = self.fac[i-1] * i % MOD
            self.inv[i] = MOD - self.inv[MOD % i] * (MOD//i) % MOD
            self.finv[i] = self.finv[i-1] * self.inv[i] % MOD

    def comb(self, n: int, r: int) -> int:
        MOD = 10**9 + 7
        if n < r:
            return 0
        if n < 0 or r < 0:
            return 0
        return self.fac[n] * (self.finv[r] * self.finv[n-r] % MOD) % MOD


H, W, A, B = list(map(int, input().split()))
c = CombinationFermat()
ans = 0
MOD = 10**9 + 7

for i in range(H-A):
    x = c.comb(B-1+i, i)
    a = H-1-i
    b = W-1-B
    x *= c.comb(a+b, a)
    x %= MOD
    ans += x
ans %= MOD
print(ans)


mod = 10**9 + 7
h, w, a, b = map(int, input().split())

fact = [1] * (h + w + 1)
invf = [1] * (h + w + 1)
invn = [1] * (h + w + 1)
for i in range(2, h + w + 1):
  fact[i] = fact[i-1] * i % mod
  invn[i] = (-invn[mod % i]) * (mod // i) % mod
  invf[i] = invf[i-1] * invn[i] % mod

count = 0
for i in range(min(h-a, w-b)):
  count += fact[h+b-a-1] * invf[h-a-i-1] * invf[b+i] * fact[w+a-b-1] * invf[a+i] * invf[w-b-i-1]
  count %= mod
print(count)

def permutation(n, k, mod):
    s = 1
    for _ in range(k):
        s *= n
        s %= mod
        n -= 1
    return s

def factorial(n, mod):
    s = 1
    for i in range(1, n + 1):
        s *= i
        s %= mod
    return s

h, w, a, b = map(int, input().split())
mod = pow(10, 9) + 7
x = h - a + b - 1
y = w - b + a - 2
p = permutation(x, h - a - 1, mod) * permutation(y, a - 1, mod) % mod
ans = p
for _ in range(w - b - 1):
    x += 1
    p = p * x * (y - (a - 1)) * pow((x - (h - a - 1)) * y, mod - 2, mod) % mod
    y -= 1
    ans += p
    ans %= mod
ans = ans * pow(factorial(a - 1, mod), mod - 2, mod) * pow(factorial(h - a - 1, mod), mod - 2, mod) % mod
print(ans)

import sys
from functools import lru_cache
sys.setrecursionlimit(10**9)

def mul(x, y, mod):
  x %= mod
  y %= mod
  return x * y % mod

def div(x, y, mod):
  x %= mod
  y %= mod
  return x * mod_pow(y, mod - 2, mod) % mod

@lru_cache(maxsize=None)
def mod_pow(a, p, mod):
  if p == 0:
    return 1
  if p % 2 == 0:
    root = mod_pow(a, p / 2, mod)
    return root * root % mod
  else:
    return a * mod_pow(a, p - 1, mod) % mod

def dnm(n, mod, factorials):
  denominators = [0] * (n + 1)
  denominators[n] = div(1, factorials, mod)
  for i in reversed(range(n)):
    denominators[i] = mul(denominators[i+1], i+1, mod)
  return denominators

def nmr(n, mod):
  factorials = [0] * (n + 1)
  factorials[0] = 1
  for i in range(n):
    factorials[i + 1] = (i + 1) * factorials[i] % mod
  return factorials

def cmb(a, b, mod, factorials, factorial_divs):
    if len(factorials) == 0:
        raise
    af = factorials[a]
    bf = factorial_divs[b]
    abf = factorial_divs[a - b]
    return mul(mul(af, bf, mod), abf, mod)

MOD=10**9+7
H,W,A,B=map(int,input().split())
ans = 0

n = nmr(H+W-2, MOD)
d = dnm(H+W-2, MOD, n[H+W-2])

for i in range(H-A):
  x = cmb(B-1+i, B-1, MOD, n, d)
  y = cmb(H+W-3-(B-1+i), W-B-1, MOD, n, d)
  ans += x * y % MOD
  ans %= MOD

print(ans)

h,w,a,b=map(int,input().split())
mod=pow(10,9)+7

# コンビネーション、さらに高速。あらかじめO(N)の計算をすることでのちの計算が早くなる
def cmb(n, r, mod):
    if ( r<0 or r>n ):
        return 0
    r = min(r, n-r)
    return g1[n] * g2[r] * g2[n-r] % mod
g1 = [1, 1] 
g2 = [1, 1] 
inverse = [0, 1]
for i in range( 2, 200000 + 1 ):
    g1.append( ( g1[-1] * i ) % mod )
    inverse.append( ( -inverse[mod % i] * (mod//i) ) % mod )
    g2.append( (g2[-1] * inverse[-1]) % mod )
ans=0
for k in range(1,h-a+1):
  tmp=cmb(k-1+b-1,k-1,mod)
  tmp*=cmb(h-k+w-b-1,h-k,mod)
  ans+=tmp
  ans%=mod
print(ans)

h, w, a, b = list(map(int, input().split()))

MOD = 1000000007


def modPow(a, x, p):
    res = 1
    while (x > 0):
        if (x % 2 != 0):
            res = (res * a) % p
        a = (a * a) % p
        x /= 2
    return res


fact = [None] * 220000

for i in range(1, 220000):
    fact[0] = 1
    fact[i] = i * fact[i - 1] % MOD
    # inv[i] = modPow(fact[i], MOD-2, MOD)


def ncr(n, r):
    den = fact[n - r] * fact[r] % MOD
    return fact[n] * pow(den, MOD - 2, MOD) % MOD


def number_of_paths(h, w):
    n = h + w - 2
    r = h - 1
    return ncr(n, r)


ans = 0
for i in range(b + 1, w + 1):
    # print('first', h-a, i)
    ans += number_of_paths(h - a, i) * number_of_paths(a, w - i + 1)

print((int(ans % MOD)))


def combmod_pre(N, p):
    '''
    sample usage:
        p = 10**9+7
        N = 10**6
        fact, finv = combmod_pre(N, p)
        combmod(n, r, p)
    '''
    fact = [1, 1]
    finv = [1, 1]
    inv = [0, 1]
    for i in range(2, N+1):
        fact.append((fact[-1] * i) % p)
        inv.append((-inv[p % i] * (p // i)) % p)
        finv.append((finv[-1] * inv[-1]) % p)
    return (fact, finv)


def combmod(n, r, fact, finv, p):
    '''
    sample usage:
        combmod(3000, 1000, fact, finv, p)
            p is a same value of combmod_pre's argument
            fact, finv is return value of combmod_pre
    '''
    if r < 0 or n < r:
        return 0
    return fact[n] * finv[r] * finv[n-r] % p


p = 10**9+7
N = 10**6
fact, finv = combmod_pre(N, p)

h, w, a, b = (int(x) for x in input().split())
ans = 0
for j in range(b, w):
    x = combmod(h - a - 1 + j, j, fact, finv, p)
    y = combmod(a + w - 2 - j, w-1 - j, fact, finv, p)
    ans += x * y
print((ans % p))




MOD = 10**9 + 7
MAX = 2*10**5
fac = [0]*MAX  # fac[n]:  (n!) mod p
finv = [0]*MAX  # finv[n]: (n!)^-1 mod p
inv = [0]*MAX  # inv[n]:  (n)^-1 mod -p


def comb_init():
    nonlocal fac, finv, inv
    fac[0] = fac[1] = 1
    finv[0] = finv[1] = 1
    inv[1] = 1
    for i in range(2, MAX):
        fac[i] = fac[i-1] * i % MOD
        inv[i] = MOD - inv[MOD % i] * (MOD//i) % MOD
        finv[i] = finv[i-1] * inv[i] % MOD


def comb(n: int, r: int) -> int:
    nonlocal fac, finv
    if n < r:
        return 0
    if n < 0 or r < 0:
        return 0
    return fac[n] * (finv[r] * finv[n-r] % MOD) % MOD


H, W, A, B = list(map(int, input().split()))
comb_init()
ans = 0

for i in range(H-A):
    x = comb(B-1+i, i)
    a = H-1-i
    b = W-1-B
    x *= comb(a+b, a)
    x %= MOD
    ans += x
ans %= MOD
print(ans)


h,w,a,b = map(int, input().split())
mx = max(h,w)
mod = 10**9+7
fac = [1]*(h+w+1)
for i in range(1,h+w+1):
	fac[i]=fac[i-1]*i%mod
rev = [1]*(mx+1)
rev[-1] = pow(fac[mx], mod-2, mod)
for i in range(mx-1, -1, -1):
	rev[i] = rev[i+1]*(i+1)%mod
const = rev[h-a-1]*rev[a-1]%mod
ans = 0
for i in range(b,w):
	ans += fac[h-a+i-1]*rev[i]*fac[a+w-2-i]*rev[w-i-1]%mod
print(ans*const%mod)

from math import comb
h,w,a,b = list(map(int,input().split()))
s = 0
nC = b-1
kC = 0
nD = w-b-1+h-1
kD = h-1
p = 1000000007
fac = [1]
ff = 1
for i in range(1,200001):
  ff *= i
  ff %= p
  fac.append(ff)
def ncr(n, r, p): 
  return (fac[n] * pow(fac[r], p-2, p) % p * pow(fac[n-r], p-2, p) % p);

for i in range(h-a):
  C = ncr(nC, kC, 1000000007)
  D = ncr(nD, kD, 1000000007)
  s = (s + C * D) % 1000000007
  nC += 1
  kC += 1
  kD -= 1
  nD -= 1
print(s)


MOD = 10 ** 9 + 7


def prepare(n):
    nonlocal MOD
    modFacts = [0] * (n + 1)
    modFacts[0] = 1
    for i in range(n):
        modFacts[i + 1] = (modFacts[i] * (i + 1)) % MOD

    invs = [1] * (n + 1)
    invs[n] = pow(modFacts[n], MOD - 2, MOD)
    for i in range(n, 1, -1):
        invs[i - 1] = (invs[i] * i) % MOD

    return modFacts, invs


def pathVar(sx, sy, gx, gy):
    x = gx - sx
    y = gy - sy
    rst = modFacts[x + y]
    rst *= invs[x] * invs[y]
    rst %= MOD
    return rst


H, W, A, B = list(map(int, input().split()))
# H -= 1; W -= 1
modFacts, invs = prepare(H + W)

cnt = 0
while A > 0 and B > 0:
    x = H - A
    y = B - 1
    path1 = pathVar(0, 0, x, y)
    path2 = pathVar(x, y, H - 1, W - 1)
    cnt += path1 * path2
    cnt %= MOD
    A -= 1; B -= 1

ans = pathVar(0, 0, H - 1, W - 1)
print(((ans - cnt) % MOD))


MOD = 10**9+7
fac = [1 for k in range(200010)]
inv = [1 for k in range(200010)]
finv = [1 for k in range(200010)]
for k in range(2,200010):
    fac[k] = (fac[k-1]*k)%MOD
    inv[k] = (MOD - inv[MOD%k] * (MOD // k))%MOD
    finv[k] = (finv[k - 1] * inv[k]) % MOD;
def nCr(n,r):
    return (fac[n]*finv[r]*finv[n-r])%MOD

H, W, A, B = list(map(int,input().split()))
ans = 0

for k in range(W-B):
    ans += nCr(A+W-B-k-2,A-1)*nCr(B+k+1+H-A-2,H-A-1)
    ans %= MOD

print(ans)


def cmb1(n,r,mod):
    if (r<0 or r>n):
        return 0
    r = min(r,n-r)
    return g1[n]*g2[r]*g2[n-r]%mod
 
h,w,a,b=map(int,input().split())
 
# 前処理
mod=10**9+7 #出力の制限
n=10**6
g1=[1,1] # 元テーブル
g2=[1,1] # 逆元テーブル
inverse=[0,1] #逆元テーブル計算用テーブル
 
for i in range(2,n+1):
    g1.append((g1[-1]*i)%mod)
    inverse.append((-inverse[mod%i]*(mod//i))%mod)
    g2.append((g2[-1]*inverse[-1])%mod)

ans=0
for i in range(b,w):
    ans+=cmb1(h-a-1+i,i,mod)*cmb1(a-1+w-1-i,a-1,mod)
    ans%=mod
print(ans)

import math

h, w, a, b = list(map(int, input().split()))

#divmod
mod = pow(10,9)+7
def divmod(num, mod=10**9+7):
    return pow(num, mod-2, mod)

#combination
def comb(a,b):
	p=fact[a-b]*fact[b]%mod
	return fact[a]*divmod(p)%mod

fact = [1]
for i in range(1,h+w):
    fact.append(i*fact[i-1]%mod)
#print(fact)

ans = 0
for j in range(h-a):
    tmp = comb(b-1+j,j)*comb(w+h-b-2-j,w-b-1)%mod
    ans += tmp
    ans = ans%mod
#    ans = ans + fact[b-1+j]*fact[w+h-b-2-j]/fact[b-1]/fact[j]/fact[w-b-1]/fact[h-1-j]
print((int(ans)))

'''
単純なh*wのマス目だった場合
#h-row / w-col
con = [[0]*w]*h
for i in range(h):
    con[i][0] = 1
for j in range(w):
    con[0][j] = 1

for k in range(1,h):
    for l in range(1,w):
        con[k][l] = con[k-1][l] + con[k][l-1]

print(con[h-1][w-1])
'''

'''
全量を計算するやり方
H*Wがデカすぎると時間というよりもメモリエラー
print('initialize')
con = [[0 for i in range(w)] for j in range(h)]
#リスト内包表記で作らないとバグる
#ダメな例 -> con = [[0]*w]*h
#https://qiita.com/utgwkk/items/5ad2527f19150ae33322
print('initialize finished')


for i in range(h-a):
    con[i][0] = 1
#print(con[0])
for j in range(w):
    #wは先に初期化やっちゃう
    con[0][j] = 1
#print(con)

for k in range(1,h-a):
#    print(k)
    for l in range(1,b+1):
        con[k][l] = con[k-1][l] + con[k][l-1]
#print(con[h-a-1][b-1])
#print(con[h-a][b-1])
#print(con[h-a-1][b])

for m in range(1,h):
#    print('---{} row---'.format(m))
#    print(con[m])
    for n in range(b,w):
#        print('m,n:('+str(m)+','+str(n)+')')
        con[m][n] = con[m-1][n] + con[m][n-1]
#    print(con[m])

print(con[h-1][w-1])
'''



g1 = [1, 1]
g2 = [1, 1]
inverse = [0, 1]
MOD = 10**9+7
for i in range(2, 2*10**5+1):
    g1.append((g1[-1] * i) % MOD)
    inverse.append((-inverse[MOD % i] * (MOD // i)) % MOD)
    g2.append((g2[-1] * inverse[-1]) % MOD)

def comb(n, r, mod=MOD):
    if r < 0 or r > n:
        return 0
    r = min(r, n - r)
    return g1[n] * g2[r] * g2[n-r] % mod

H, W, A, B = map(int, input().split())
ans = 0
n = H + W - B - 1
for i in range(1, H-A+1):
  ans += comb(n-i, H-i) * comb(B+i-2, B-1) % MOD
  ans %= MOD

print(ans)

import sys, re
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, tan, asin, acos, atan, radians, degrees, log2
from itertools import accumulate, permutations, combinations, combinations_with_replacement, product, groupby
from operator import itemgetter, mul
from copy import deepcopy
from string import ascii_lowercase, ascii_uppercase, digits
from bisect import bisect, bisect_left
from heapq import heappush, heappop
from functools import reduce
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return list(map(int, input().split()))
def LIST(): return list(map(int, input().split()))
def ZIP(n): return list(zip(*(MAP() for _ in range(n))))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7

lim = 2*10**6
fact = [1]*(lim+1)
for n in range(1, lim+1):
	fact[n] = n*fact[n-1]%mod

fact_inv = [1]*(lim+1)
fact_inv[lim] = pow(fact[lim], mod-2, mod)
for n in range(lim, 0, -1):
	fact_inv[n-1] = n*fact_inv[n]%mod

def C(n, r):
	return (fact[n]*fact_inv[r]%mod)*fact_inv[n-r]%mod

H, W, A, B = MAP()

ans = 0
for n in range(B, W):
	way = C(H-A-1+n, n)*C(W-n-1+A-1, A-1)%mod
	ans = (ans+way)%mod

print(ans)


import math
p=1000000007
g1=[1,1]
g2=[1,1]
inverse=[0,1]
for i in range(2,2*(10**5)+1):
    g1.append((g1[-1]*i)%p)
    inverse.append((-inverse[p%i]*(p//i))%p)
    g2.append((g2[-1]*inverse[-1])%p)
def cmb2(n, r, mod):
    if (r<0 or r>n):return 0
    r = min(r,n-r)
    return g1[n]*g2[r]*g2[n-r]%mod
def chwp(h,w,p):
    if h==1 or w==1:return 1
    else:return cmb2(h+w-2,h-1,p)
h,w,a,b= map(int,input().split())
ans=0
for i in range(1,h-a+1):ans=(ans+chwp(i,b,p)*chwp(h-i+1,w-b,p))%p
print(ans)

import sys
from functools import lru_cache
sys.setrecursionlimit(10**9)
 
def mul(x, y, mod):
  x %= mod
  y %= mod
  return x * y % mod
 
def div(x, y, mod):
  x %= mod
  y %= mod
  return x * mod_pow(y, mod - 2, mod) % mod
 
@lru_cache(maxsize=None)
def mod_pow(a, p, mod):
  if p == 0:
    return 1
  if p % 2 == 0:
    root = mod_pow(a, p / 2, mod)
    return root * root % mod
  else:
    return a * mod_pow(a, p - 1, mod) % mod
 
def dnm(n, mod, factorials):
  denominators = [0] * (n + 1)
  denominators[n] = div(1, factorials, mod)
  for i in reversed(range(n)):
    denominators[i] = mul(denominators[i+1], i+1, mod)
  return denominators
 
def nmr(n, mod):
  factorials = [0] * (n + 1)
  factorials[0] = 1
  for i in range(n):
    factorials[i + 1] = (i + 1) * factorials[i] % mod
  return factorials
 
def cmb(a, b, mod, factorials, factorial_divs):
    if len(factorials) == 0:
        raise
    af = factorials[a]
    bf = factorial_divs[b]
    abf = factorial_divs[a - b]
    return mul(mul(af, bf, mod), abf, mod)
 
MOD=10**9+7
H,W,A,B=map(int,input().split())
ans = 0
 
n = nmr(H+W-2, MOD)
d = dnm(H+W-2, MOD, n[H+W-2])
 
for i in range(H-A):
  x = cmb(B-1+i, B-1, MOD, n, d)
  y = cmb(H+W-3-(B-1+i), W-B-1, MOD, n, d)
  ans += x * y % MOD
  ans %= MOD
 
print(ans)

class Combination():
    # コンストラクタ
    def __init__(self, N:int, P:int):
        self.N = N
        self.P = P

        # fact[i] = (i! mod P)
        self.fact = [1, 1]   
        # factinv[i] = ((i!)^(-1) mod P)
        self.factinv = [1, 1]
        # factinv 計算用
        self.inv = [0, 1]    

        for i in range(2, N+1):
            self.fact.append((self.fact[-1] * i) % P)
            self.inv.append((-self.inv[P % i] * (P // i)) % P)
            self.factinv.append((self.factinv[-1] * self.inv[-1]) % P)
    
    # nCk (mod P)   (ただし、n<=N)
    def getComb(self, n:int, k:int):
        if (k < 0) or (n < k):
            return 0
        k = min(k, n - k)
        return self.fact[n] * self.factinv[k] * self.factinv[n-k] % self.P

def main():
    H,W,A,B = map(int,input().split())
    MOD = 10**9 + 7

    COMB = Combination(H+W, MOD)

    # (1,1) -> (i,B-1) -> (i,B+1) -> (H,W)

    ans = 0
    for i in range(1,H-A+1):
        tmp = COMB.getComb((i-1)+(B-1), i-1)
        tmp *= COMB.getComb((H-i)+(W-B-1), H-i)
        ans = (ans + tmp) % MOD

    print(ans)

def __starting_point():
    main()
__starting_point()