High school student Vasya got a string of length n as a birthday present. This string consists of letters ‘a’ and ‘b’ only. Vasya denotes beauty of the string as the maximum length of a substring (consecutive subsequence) consisting of equal letters.

Vasya can change no more than k characters of the original string. What is the maximum beauty of the string he can achieve?

Input
The first line of the input contains two integers n and k (1?≤?n?≤?100?000,?0?≤?k?≤?n) — the length of the string and the maximum number of characters to change.

The second line contains the string, consisting of letters ‘a’ and ‘b’ only.

Output
Print the only integer — the maximum beauty of the string Vasya can achieve by changing no more than k characters.

Examples
Input
4 2
abba
Output
4
Input
8 1
aabaabaa
Output
5
Note
In the first sample, Vasya can obtain both strings “aaaa” and “bbbb”.

In the second sample, the optimal answer is obtained with the string “aaaaabaa” or with the string “aabaaaaa”.
思路：因為只有兩種字母，因此我們分開考慮，一次把’a’換成’b’，另外一次倒過來。在換字母的時候，主要方法就是尺取法了。細節有一點多，需要多考慮一下。
代碼如下：

#include<bits/stdc++.h> #define ll long long using namespace std;const int maxx=1e5+100; string s; int n,k;inline int fcs(char c) {int l=0,r=0;int _max=0,sum=0;while(r<n){while(sum<=k&&r<n){if(s[r]==c) sum++;r++;}if(sum>k) r--,sum--;_max=max(_max,r-l);while(sum>=k&&l<n){if(s[l]==c) sum--;l++;}}return _max; } int main() {scanf("%d%d",&n,&k);cin>>s;printf("%d\n",max(fcs('a'),fcs('b')));return 0; }

努力加油a啊，(^o)/~

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