2 pointer

import java.io.*;
import java.util.*;

public class Codeforces
{
    public static void main(String args[])throws Exception
    {
        BufferedReader bu=new BufferedReader(new InputStreamReader(System.in));
        StringBuilder sb=new StringBuilder();
        String s[]=bu.readLine().split(" ");
        int n=Integer.parseInt(s[0]),i,l=0,c[]=new int[26],ans=0;
        long x=Long.parseLong(s[1]),cur=0;
        char a[]=bu.readLine().toCharArray();
        for(i=0;i<n;i++)
        {
            int y=a[i]-'a';
            c[y]++;
            if(y==1) cur+=c[0];
            while(cur>x)
            {
                y=a[l++]-'a';
                c[y]--;
                if(y==0) cur-=c[1];
            }
            ans=Math.max(ans,i-l+1);
        }
        System.out.println(ans);
    }
}