#include<bits/stdc++.h>
using namespace std;
#define int long long
string s;
signed main(){
	int k;
	char c1,c2;
	cin >> k >> s >> c1 >> c2;
	int n = s.size();
	int ans = 0 ,cnt = 0;
	for(int i = 0, j = k - 1; j < n; i++,j++){
		if(s[i] == c1) cnt++;
		if(s[j] == c2) ans += cnt;
	}
	cout << ans;
	return 0;
}