- Time limit: 1.00 s
- Memory limit: 512 MB
For example, when $n=6$ and $k=4$, some valid sequences are $[1,3,1,4,3,2]$ and $[2,2,1,3,4,2]$.
Input
The only input line has two integers $n$ and $k$.
Output
Print one integer: the number of sequences modulo $10^9+7$.
Constraints
- $1 \le k \le n \le 10^6$
Input:
6 4
Output:
1560