CSES - Counting Bishops
  • Time limit: 1.00 s
  • Memory limit: 512 MB
Your task is to count the number of ways $k$ bishops can be placed on an $n \times n$ chessboard so that no two bishops attack each other.

Two bishops attack each other if they are on the same diagonal.

Input

The only input line has two integers $n$ and $k$: the board size and the number of bishops.

Output

Print one integer: the number of ways modulo $10^9+7$.

Constraints
  • $1 \le n \le 500$
  • $1 \le k \le n^2$
Example

Input:
5 4

Output:
2728