#D24. Almost Identity Permutations
Almost Identity Permutations
Almost Identity Permutations
A permutation p of size n is an array such that every integer from 1 to n occurs exactly once in this array.
Let's call a permutation an almost identity permutation iff there exist at least n - k indices i (1 ≤ i ≤ n) such that pi = i.
Your task is to count the number of almost identity permutations for given numbers n and k.
Input
The first line contains two integers n and k (4 ≤ n ≤ 1000, 1 ≤ k ≤ 4).
Output
Print the number of almost identity permutations for given n and k.
Examples
Input
4 1
Output
1
Input
4 2
Output
7
Input
5 3
Output
31
Input
5 4
Output
76
inputFormat
Input
The first line contains two integers n and k (4 ≤ n ≤ 1000, 1 ≤ k ≤ 4).
outputFormat
Output
Print the number of almost identity permutations for given n and k.
Examples
Input
4 1
Output
1
Input
4 2
Output
7
Input
5 3
Output
31
Input
5 4
Output
76
样例
4 2
7