CF578D.LCS Again

普及/提高-

通过率：0%

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题目描述

You are given a string $S$ of length $n$ with each character being one of the first $m$ lowercase English letters.

Calculate how many different strings $T$ of length $n$ composed from the first $m$ lowercase English letters exist such that the length of LCS (longest common subsequence) between $S$ and $T$ is $n-1$ .

Recall that LCS of two strings $S$ and $T$ is the longest string $C$ such that $C$ both in $S$ and $T$ as a subsequence.

输入格式

The first line contains two numbers $n$ and $m$ denoting the length of string $S$ and number of first English lowercase characters forming the character set for strings ( $1<=n<=100000$ , $2<=m<=26$ ).

The second line contains string $S$ .

输出格式

Print the only line containing the answer.

输入输出样例

输入#1
```
3 3
aaa
```
输出#1
```
6
```
输入#2
```
3 3
aab
```
输出#2
```
11
```
输入#3
```
1 2
a
```
输出#3
```
1
```
输入#4
```
10 9
abacadefgh
```
输出#4
```
789
```

说明/提示

For the first sample, the $6$ possible strings $T$ are: aab, aac, aba, aca, baa, caa.

For the second sample, the $11$ possible strings $T$ are: aaa, aac, aba, abb, abc, aca, acb, baa, bab, caa, cab.

For the third sample, the only possible string $T$ is b.

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