G

#include <bits/stdc++.h>


using namespace std;

#define int long long

const long long INF = 1e9 + 7;
const int MAXN = 200 + 10;
const int N = 1e5 + 10;

int Sum(int a1, int n, int d) {
    return (2 * a1 + d * (n - 1)) * n / 2;
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    int n, c;
    cin >> n >> c;
    string s;
    cin >> s;

    vector<int> sum_a(n + 1, 0), sum_b(n + 1, 0);
    for (int i = 0; i < n; ++i) {
        sum_a[i + 1] = sum_a[i] + (s[i] == 'a' ? 1 : 0);
        sum_b[i + 1] = sum_b[i] + (s[i] == 'b' ? 1 : 0);
    }

    int cost = 0, ans = 0;
    int l = 0;
    for (int r = 0; r < n; ++r) {
        if (s[r] == 'b') {
            cost += sum_a[r + 1] - sum_a[l];
        }
        while (cost > c && l <= r) {
            if (s[l] == 'a') {
                cost -= sum_b[r + 1] - sum_b[l];
            }
            ++l;
        }
        ans = max(ans, r - l + 1);
    }
    cout << ans << '\n';
}