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题库练习 Almost Identity Permutations

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A11423 | $Almost Identity Permutations$

时间限制1s

内存限制256MB

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题目描述

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 $p_{i}=i$ . Your task is to count the number of almost identity permutations for given numbers $n$ and $k$ .

输入格式

The first line contains two integers $n$ and $k$ ( $4<=n<=1000$ , $1<=k<=4$ ).

输出格式

Print the number of almost identity permutations for given $n$ and $k$ .

输入输出样例

输入 #1

4 1

输出 #1

输入 #2

4 2

输出 #2

输入 #3

5 3

输出 #3

输入 #4

5 4

输出 #4

C++ 编辑器

输入

输出