#include <bits/stdc++.h>
using namespace std;
#define debug(x) cout << #x << " = " << x << endl;
#define debugPair(x, y) cout << #x << " = " << x << ", " << #y << " = " << y << endl
#define debugTuple(x, y, z) cout << #x << " = " << x << ", " << #y << " = " << y << ", " << #z << " = " << z << endl
#define debugArray(arr, n, m)         \
    cout << #arr << endl;             \
    for (int i = 1; i <= n; i++)      \
    {                                 \
        for (int j = 1; j <= m; j++)  \
        {                             \
            cout << arr[i][j] << " "; \
        }                             \
        cout << endl;                 \
    }                                 \
    cout << endl
typedef long long ll;
const int N = 5e5 + 5;
const int INF = 0x3f3f3f;
int cnt[N];
int lastc1 = -1;
char c1, c2;
string s;
int k;
ll res = 0;
void solve()
{
    cin >> k;
    cin >> s;
    cin >> c1 >> c2;
    int l = s.size();
    for (int i = 0; i < l; i++)
    {
        char c = s[i];
        cnt[i]+=cnt[i - 1];
        if (c == c1)
        {
            cnt[i]++;
        }
        if (c == c2)
        {
            int pre = i-k+1;
            if(pre>=0){
                res+=cnt[pre];
            }       
        }
    }

    cout << res << endl;
}
signed main()
{
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    solve();
    return 0;
}