#include <bits/stdc++.h>


using namespace std;

//#define int long long

const long long INF = 1e18 + 7;
const int MAXN = 5e3 + 10;
const int N = 1e5 + 10;

unsigned short int cnt[MAXN][MAXN];

void solve() {
    int n, k;
    cin >> n >> k;
    string s;
    cin >> s;
    for (int i = 0; i < n - 1; ++i) {
        cnt[i][i + 1] = (s[i] == s[i + 1] ? 0 : 1);
    }
    for (int len = 3; len <= n; ++len) {
        for (int l = 0; l + len - 1 < n; ++l) {
            int r = l + len - 1;
            cnt[l][r] = cnt[l + 1][r - 1] + (s[l] == s[r] ? 0: 1);
        }
    }
    long long ans = n;
    for (int len = 2; len <= n; ++len) {
        for (int l = 0; l + len - 1 < n; ++l) {
            int r = l + len - 1;
            if (cnt[l][r] <= k) {
                ++ans;
            }
        }
    }
    cout << ans << '\n';
}

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

    int tt = 1;
//    cin >> tt;
    while (tt--) {
        solve();
    }
}