#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

const int N = 500010;

int n, k;
char a, b, s[N];

int main() {
    cin >> k >> s + 1 >> a >> b;

    n = strlen(s + 1);
    long long ans = 0;
    int cnt = 0;
    for (int i = k; i <= n; i ++ ) {
        if (s[i - k + 1] == a) cnt ++ ;
        if (s[i] == b) ans += cnt;
    }

    cout << ans;

    return 0;
}