- Time limit: 1.00 s
- Memory limit: 512 MB
Two bishops attack each other if they are on the same diagonal.
The only input line has two integers $n$ and $k$: the board size and the number of bishops.
Print one integer: the number of ways modulo $10^9+7$.
- $1 \le n \le 500$
- $1 \le k \le n^2$