Buggy python submission (verdict: Runtime Error):
import sys
input = sys.stdin.readline
from collections import deque
import math

def main():
    x,y=map(int,input().split())
    MOD=10**9+7
    if (x+y)%3!=0:
        print(0)
    else:
        n=int((x+y)/3)
        k=int((2*x-y)/3)
    a,b=1,1
    for i in range(k):
        a=(a*(n-i))%MOD
        b=(b*(1+i))%MOD
    ans=(a*pow(b,MOD-2,MOD))%MOD
    print(int(ans))

if __name__ == '__main__':
    main()

Fixed submission:
import sys
input = sys.stdin.readline
from collections import deque
import math

def main():
    def pre(n,MOD):
        a=1
        for i in range(1,n+1):
            a=(a*i)%MOD
        an=a
        b=pow(a,MOD-2,MOD)
        bs=[1]*(n+1)
        bs[n]=b
        for i in range(n,1,-1):
            b=b*i%MOD
            bs[i-1]=b
        return an,bs
    
    x,y=map(int,input().split())
    d=(x+y)//3
    MOD=10**9+7
    if (x+y)%3!=0 or x<d or y<d:
        print(0)
    else:
        a,b=pre(d,MOD)
        a=a*b[y-d]*b[2*d-y]%MOD
        print(a)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Runtime Error):
import sys
input = sys.stdin.readline
from collections import deque

def main():
    x,y=map(int,input().split())
    MOD=10**9+7
    if (x+y)%3!=0:
        print(0)
    else:
        n=int((x+y)/3)
        k=int((2*x-y)/3)
    a,b=1,1
    for i in range(k):
        a=(a*(n-i))%MOD
        b=(b*(1+i))%MOD
    ans=(a*pow(b,MOD-2,MOD))%MOD
    print(int(ans))
    
if __name__ == '__main__':
    main()

Fixed submission:
import sys
input = sys.stdin.readline
from collections import deque
import math

def main():
    def pre(n,MOD):
        a=1
        for i in range(1,n+1):
            a=(a*i)%MOD
        an=a
        b=pow(a,MOD-2,MOD)
        bs=[1]*(n+1)
        bs[n]=b
        for i in range(n,1,-1):
            b=b*i%MOD
            bs[i-1]=b
        return an,bs
    
    x,y=map(int,input().split())
    d=(x+y)//3
    MOD=10**9+7
    if (x+y)%3!=0 or x<d or y<d:
        print(0)
    else:
        a,b=pre(d,MOD)
        a=a*b[y-d]*b[2*d-y]%MOD
        print(a)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Runtime Error):
import sys
input = sys.stdin.readline
from collections import deque

def main():
    x,y=map(int,input().split())
    MOD=10**9+7
    if (x+y)%3!=0:
        print(0)
    else:
        n=int((x+y)/3)
        k=int((2*x-y)/3)
    a,b=1,1
    for i in range(k):
        a=(a*(n-i))%MOD
        b=(b*(1+i))%MOD
    ans=(a*pow(b,MOD-2,MOD))%MOD
    print(int(ans))
    
if __name__ == '__main__':
    main()

Fixed submission:
import sys
input = sys.stdin.readline
from collections import deque
import math

def main():
    def pre(n,MOD):
        a=1
        for i in range(1,n+1):
            a=(a*i)%MOD
        an=a
        b=pow(a,MOD-2,MOD)
        bs=[1]*(n+1)
        bs[n]=b
        for i in range(n,1,-1):
            b=b*i%MOD
            bs[i-1]=b
        return an,bs
    
    x,y=map(int,input().split())
    d=(x+y)//3
    MOD=10**9+7
    if (x+y)%3!=0 or x<d or y<d:
        print(0)
    else:
        a,b=pre(d,MOD)
        a=a*b[y-d]*b[2*d-y]%MOD
        print(a)

if __name__ == '__main__':
    main()