Iroha is on a grid with H rows and W columns. She starts at the top-left cell and moves right or down to reach the bottom-right cell. She cannot enter the bottom A rows and leftmost B columns. Find the number of ways she can reach the bottom-right cell, modulo 10^9+7. Constraints: 1 ≤ H, W ≤ 100,000, 1 ≤ A < H, 1 ≤ B < W. Input format: H W A B. Output: Number of ways to reach the bottom-right cell, modulo 10^9+7. Example: Input: 2 3 1 1, Output: 2. Example: Input: 10 7 3 4, Output: 3570. Example: Input: 100000 100000 99999 99999, Output: 1. Example: Input: 100000 100000 44444 55555, Output: 738162020.

# Buggy version:

mod = 10**9+7


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


class Fact():
    def __init__(self, H, W):
        self.mod = 10**9+7
        self.facts = [1]*(H+W-1)
        for i in range(1, H+W-1):
            self.facts[i] = self.facts[i-1]*i % mod

        self.i = [pow(self.facts[-1], mod-2, mod)]
        for i in range(1, H+W-1)[::-1]:
            self.i.append(self.i[-1]*i % mod)
        self.i.reverse()

    def comb(self, n, r):
        ret = self.facts[n] * self.i[n-r]*self.i[r]
        return ret

    def print_fact(self):
        print(self.facts)


f = Fact(H, W)

all_path = f.comb(H+W-2, H-1)

f.print_fact()

remove_path = 0
for i in range(B):
    tmp = f.comb(H-A+i-1, i)
    tmp *= f.comb(W-i-1+A-1, A-1)
    remove_path += tmp

remove_path %= mod

print((all_path - remove_path) % mod)


# Fixed version:
mod = 10**9+7


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


class Fact():
    def __init__(self, H, W):
        self.mod = 10**9+7
        self.facts = [1]*(H+W-1)
        for i in range(1, H+W-1):
            self.facts[i] = self.facts[i-1]*i % mod

        self.i = [pow(self.facts[-1], mod-2, mod)]
        for i in range(1, H+W-1)[::-1]:
            self.i.append(self.i[-1]*i % mod)
        self.i.reverse()

    def comb(self, n, r):
        ret = self.facts[n] * self.i[n-r]*self.i[r]
        return ret

    def print_fact(self):
        print(self.facts)


f = Fact(H, W)

all_path = f.comb(H+W-2, H-1)

remove_path = 0
for i in range(B):
    tmp = f.comb(H-A+i-1, i)
    tmp *= f.comb(W-i-1+A-1, A-1)
    remove_path += tmp

remove_path %= mod

print((all_path - remove_path) % mod)

# Buggy version:
ai = lambda: list(map(int,input().split()))

mod = 10**9+7


def nCb(n, b):
    if b > n - b:
        b = n - b
    r = 1
    for k in range(n, n-b, -1):
        r = r * k % mod
    d = 1
    for k in range(1, b+1):
        d = d * k % mod
    return r * inv(d) % mod


def inv(x):
    return pow(x, mod - 2, mod)


h,w,a,b = ai()
ans = 0
c1 = nCb(b-1,0)
c2 = nCb(w-b+h-2, h-1)
for i in range(h-a):
    ans += c1 * c2
    ans %= mod
    c1 = c1 * (b+i) // (i+1)
    c2 = c2 * (h-i-1) // (w-b+h-i-2)
print(ans)


# Fixed version:
ai = lambda: list(map(int,input().split()))

mod = 10**9+7


def nCb(n, b):
    if b > n - b:
        b = n - b
    r = 1
    for k in range(n, n-b, -1):
        r = r * k % mod
    d = 1
    for k in range(1, b+1):
        d = d * k % mod
    return r * inv(d) % mod


def inv(x):
    return pow(x, mod - 2, mod)


h,w,a,b = ai()
aa = h-a-1
bb = w-b-1
c1 = nCb(aa+b, b)
c2 = nCb(a+bb-1, bb)
ans = c1 * c2
ans %= mod

for i in range(1, bb+1):
    c1 = c1 * (aa + b + i) * inv(b + i) % mod
    c2 = c2 * (bb - i + 1) * inv(a + bb - i) % mod
    ans += c1 * c2
    ans %= mod
print(ans)

# Buggy version:
BIG = (10 ** 9) + 7

f_list = [1] * 200000
f_r_list = [1] * 200000

for i in range(199999):
	f_list[i + 1] = int((f_list[i] * (i + 2)) % BIG)

def power(n, x):
	if x == 1:
		return n
	elif x % 2 == 0:
		return power(int((n * n) % BIG), int(x / 2))
	else:
		return int((n * power(n, x - 1)) % BIG)

for i in range(200000):
	f_r_list[i] = power(f_list[i], BIG - 2)

def comb(n, r):
	if n == 0 or r == 0 or n == r:
		return 1
	else:
		return (((f_list[n - 1] * f_r_list[n - r - 1]) % BIG) * f_r_list[r - 1]) % BIG 

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

ans = 0

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

print(int(ans))

# Fixed version:
BIG = (10 ** 9) + 7

f_list = [1] * 200000
f_r_list = [1] * 200000

for i in range(199999):
	f_list[i + 1] = int((f_list[i] * (i + 2)) % BIG)

def power(n, x):
	if x == 1:
		return n
	elif x % 2 == 0:
		return power(int((n * n) % BIG), int(x / 2))
	else:
		return int((n * power(n, x - 1)) % BIG)

f_r_list[-1] = power(f_list[-1], BIG - 2)

for i in range(2, 200001):
	f_r_list[-i] = int((f_r_list[-i + 1] * (200002 - i)) % BIG)

def comb(n, r):
	if n == 0 or r == 0 or n == r:
		return 1
	else:
		return (((f_list[n - 1] * f_r_list[n - r - 1]) % BIG) * f_r_list[r - 1]) % BIG 

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

ans = 0

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

print(int(ans))

# Buggy version:
import scipy.misc as scm

H, W, A, B = [int(input()) for _ in range(4)]
MOD = 10**9 + 7
f = [1]
a = [1]
for i in range(1, H+W-1):
    f.append((f[i-1] * i) % MOD)
    a.append(pow(f[i], MOD-2, MOD))
ans = 0
for i in range(B, W, 1):
    ans += (((f[(H-A-1)+i] * a[H-A-1] * a[i]) % MOD) * ((f[(A-1)+(W-1-i)] * a[A-1] * a[W-1-i]) % MOD))
    ans %= MOD
print(ans)

# Fixed version:
import scipy.misc as scm

H, W, A, B = [int(i) for i in input().split()]
MOD = 10**9 + 7
f = [1]
a = [1]
for i in range(1, H+W-1):
    f.append((f[i-1] * i) % MOD)
    a.append(pow(f[i], MOD-2, MOD))
ans = 0
for i in range(B, W, 1):
    ans += (((f[(H-A-1)+i] * a[H-A-1] * a[i]) % MOD) * ((f[(A-1)+(W-1-i)] * a[A-1] * a[W-1-i]) % MOD))
    ans %= MOD
print(ans)