- Time limit: 1.00 s
- Memory limit: 512 MB
For example, when $n=4$ and $k=3$, there are $6$ such permutations:
- $[1,4,3,2]$
- $[2,3,4,1]$
- $[2,4,1,3]$
- $[3,1,4,2]$
- $[3,2,1,4]$
- $[4,1,2,3]$
The only input line has two integers $n$ and $k$.
Output
Print the answer modulo $10^9+7$.
Constraints
- $1 \le n \le 500$
- $0 \le k \le \frac{n(n-1)}{2}$
Input:
4 3
Output:
6