Solve in Python:
There is a knight - the chess piece - at the origin (0, 0) of a two-dimensional grid.
When the knight is at the square (i, j), it can be moved to either (i+1,j+2) or (i+2, j+1).
In how many ways can the knight reach the square (X, Y)?
Find the number of ways modulo 10^9 + 7.

-----Constraints-----
 - 1 \leq X \leq 10^6
 - 1 \leq Y \leq 10^6
 - All values in input are integers.

-----Input-----
Input is given from Standard Input in the following format:
X Y

-----Output-----
Print the number of ways for the knight to reach (X, Y) from (0, 0), modulo 10^9 + 7.

-----Sample Input-----
3 3

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

There are two ways: (0,0) \to (1,2) \to (3,3) and (0,0) \to (2,1) \to (3,3).
X,Y = map(int,input().split())
mod = 10**9+7
N = (X+Y)//3
M = (N+X-Y)//2

if (X+Y)%3!=0 or M<0 or N<M:
  print(0)
else:
  ans = 1
  for m in range(1,M+1):
    ans*=(N-M+m)*pow(m,mod-2,mod)
    ans%=mod
  print(ans)