//  lanqiao3514 字串简写(前缀和优化)
#include<bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
    int k;
    string s;
    char a, b;
    cin >> k >> s >> a >> b;
    int ft = 0;
    int bk = 0;
    for(int i = 0, j = k - 1; j < s.size(); i++, j++){
        if(s[i] == a) ft++;
        if(s[j] == b) bk += ft;
    }
    cout << bk << endl;
}
/* samples -> 6
4
abababdb a b
*/