#include "bits/stdc++.h"
using namespace std;

const int N = 100010;
int n,k; //n = number of characters and k = how many character's you can change
int pa[N],pb[N]; //pa => prefix sum of a,pb => pref sum of b

bool yes (int x) {
	int L = 1,R = x;
	while (R <= n) {
		int a = pa[R] - pa[L - 1];
		int b = pb[R] - pb[L - 1];
		int m = min(a,b);
		if (m <= k) {
			//~ cout << L << ' ' << R << '\n';
			return true;
		}
		L++,R++;
	}
	//asbei na
	return false;
}

//1) calc pref
//2) bin search
//3) implement yes function

int main () {
	 ios::sync_with_stdio(false);
	 cin.tie(nullptr);
	 cout.tie(nullptr);
	 string s;
	 cin >> n >> k >> s;
	 int a[n + 1],b[n + 1];//if ith pos contain a 1 otherwise 0
	 a[0] = 0,b[0] = 0;
	 for (int i = 0; i < n; ++i) {
		 if (s[i] == 'a') {
			 a[i + 1] = 1;
		 } else {
			 a[i + 1] = 0;
		 }
	 }
	 for (int i = 0; i < n; ++i) {
		 if (s[i] == 'b') {
			 b[i + 1] = 1;
		 } else {
			 b[i + 1] = 0;
		 }
	 }
	 for (int i = 1; i <= n; ++i) {
		 pa[i] = pa[i - 1] + a[i];
	 }
	 for (int i = 1; i <= n; ++i) {
		 pb[i] = pb[i - 1] + b[i];
	 }
	 int l = 1,r = n;
	 int res = 0;
	 while (l <= r) {
		 int mid = (l + r) / 2;
		 if (yes(mid)) {
			 res = mid;
			 l = mid + 1;
		 } else {
			 r = mid - 1;
		 }
	 }
	 cout << res << '\n';
}

//Problem Link : https://codeforces.com/contest/676/problem/C