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).

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