#include <bits/stdc++.h>
using u32 = unsigned;
using i64 = long long;
using u64 = unsigned long long;
const int N = 5e5 + 10;
i64 sum[N];
int main()
{
    int k;
    std::cin >> k;
    std::string str;
    std::cin >> str;
    char c1, c2;
    std::cin >> c1 >> c2;
    i64 res = 0;
    for (int i = 1; i < str.size(); i ++) {
        sum[i] = sum[i-1] + (str[i] == c2);
    }
    for (int i = 0; (i + k - 1) < str.size(); i ++) {
        if (str[i] == c1) {
            res += sum[str.size() - 1] - sum[i + k - 2];
        }
    }
    std::cout << res << "\n";
    return 0;
}