#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;
}
厉害