B

#include <cstdio>
#include <iostream>
#include <string>

using namespace std;

int main() {
    int n, k;
    string s;
    cin >> n >> k >> s;

    int res = n;

    for (int i = 0; i + 2 < n; i++) {
        int sum = 0;
        for (int j = 0; i - j >= 0 && i + 2 + j < n; j++) {
            if (s[i - j] != s[i + 2 + j]) sum++;
            if (sum > k) break;
            res++;
        }
    }

    for (int i = 0; i + 1 < n; i++) {
        int sum = 0;
        for (int j = 0; i - j >= 0 && i + 1 + j < n; j++) {
            if (s[i - j] != s[i + 1 + j]) sum++;
            if (sum > k) break;
            res++;
        }
    }

    cout << res << endl;

    return 0;
}