Buggy python submission (verdict: Time Limit Exceeded):
from math import ceil,floor,factorial,gcd,sqrt,log2,cos,sin,tan,acos,asin,atan,degrees,radians,pi,inf
from itertools import accumulate,groupby,permutations,combinations,product,combinations_with_replacement
from collections import deque,defaultdict,Counter
from bisect import bisect_left,bisect_right
from operator import itemgetter
from heapq import heapify,heappop,heappush
from queue import Queue,LifoQueue,PriorityQueue
from copy import deepcopy
from time import time
import string
import sys
sys.setrecursionlimit(10 ** 7)
def input() : return sys.stdin.readline().strip()
def INT()   : return int(input())
def MAP()   : return map(int,input().split())
def LIST()  : return list(MAP())

def cmb(n,k,p):
  """power_funcを用いて(nCk) mod p を求める"""
  from math import factorial
  if n<0 or k<0 or n<k: return 0
  if n==0 or k==0: return 1
  a=factorial(n) %p
  b=factorial(k) %p
  c=factorial(n-k) %p
  return (a*power_func(b,p-2,p)*power_func(c,p-2,p))%p
def power_func(a,b,p):
  """a^b mod p を求める"""
  if b==0: return 1
  if b%2==0:
    d=power_func(a,b//2,p)
    return d*d %p
  if b%2==1:
    return (a*power_func(a,b-1,p))%p

x, y = MAP()
a = 2*x - y
b = 2*y - x

if a >= 0 and b >= 0 and a % 3 == 0 and b % 3 == 0:
    a //= 3
    b //= 3
    ans = cmb(a+b, a, 10**9+7)
else:
    ans = 0

print(ans)

Fixed submission:
from math import ceil,floor,factorial,gcd,sqrt,log2,cos,sin,tan,acos,asin,atan,degrees,radians,pi,inf,comb
from itertools import accumulate,groupby,permutations,combinations,product,combinations_with_replacement
from collections import deque,defaultdict,Counter
from bisect import bisect_left,bisect_right
from operator import itemgetter
from heapq import heapify,heappop,heappush
from queue import Queue,LifoQueue,PriorityQueue
from copy import deepcopy
from time import time
import string
import sys
sys.setrecursionlimit(10 ** 7)
def input() : return sys.stdin.readline().strip()
def INT()   : return int(input())
def MAP()   : return map(int,input().split())
def LIST()  : return list(MAP())

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 )

x, y = MAP()
a = 2*x - y
b = 2*y - x

if a >= 0 and b >= 0 and a % 3 == 0 and b % 3 == 0:
    a //= 3
    b //= 3
    ans = cmb(a+b, a, 10**9+7)
else:
    ans = 0

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from math import ceil,floor,factorial,gcd,sqrt,log2,cos,sin,tan,acos,asin,atan,degrees,radians,pi,inf,comb
from itertools import accumulate,groupby,permutations,combinations,product,combinations_with_replacement
from collections import deque,defaultdict,Counter
from bisect import bisect_left,bisect_right
from operator import itemgetter
from heapq import heapify,heappop,heappush
from queue import Queue,LifoQueue,PriorityQueue
from copy import deepcopy
from time import time
import string
import sys
sys.setrecursionlimit(10 ** 7)
def input() : return sys.stdin.readline().strip()
def INT()   : return int(input())
def MAP()   : return map(int,input().split())
def LIST()  : return list(MAP())

def cmb(n,k,p):
  """power_funcを用いて(nCk) mod p を求める"""
  from math import factorial
  if n<0 or k<0 or n<k: return 0
  if n==0 or k==0: return 1
  a=factorial(n) %p
  b=factorial(k) %p
  c=factorial(n-k) %p
  return (a*power_func(b,p-2,p)*power_func(c,p-2,p))%p
def power_func(a,b,p):
  """a^b mod p を求める"""
  if b==0: return 1
  if b%2==0:
    d=power_func(a,b//2,p)
    return d*d %p
  if b%2==1:
    return (a*power_func(a,b-1,p))%p

x, y = MAP()
a = 2*x - y
b = 2*y - x

if a >= 0 and b >= 0 and a % 3 == 0 and b % 3 == 0:
    a //= 3
    b //= 3
    ans = cmb(a+b, a, 10**9+7)
else:
    ans = 0

print(ans)

Fixed submission:
from math import ceil,floor,factorial,gcd,sqrt,log2,cos,sin,tan,acos,asin,atan,degrees,radians,pi,inf,comb
from itertools import accumulate,groupby,permutations,combinations,product,combinations_with_replacement
from collections import deque,defaultdict,Counter
from bisect import bisect_left,bisect_right
from operator import itemgetter
from heapq import heapify,heappop,heappush
from queue import Queue,LifoQueue,PriorityQueue
from copy import deepcopy
from time import time
import string
import sys
sys.setrecursionlimit(10 ** 7)
def input() : return sys.stdin.readline().strip()
def INT()   : return int(input())
def MAP()   : return map(int,input().split())
def LIST()  : return list(MAP())

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 )

x, y = MAP()
a = 2*x - y
b = 2*y - x

if a >= 0 and b >= 0 and a % 3 == 0 and b % 3 == 0:
    a //= 3
    b //= 3
    ans = cmb(a+b, a, 10**9+7)
else:
    ans = 0

print(ans)