F

#include <bits/stdc++.h>


using namespace std;

#define int long long

const long long INF = 1e9 + 7;
const int MAXN = 200 + 10;
const int N = 1e5 + 10;

int Sum(int a1, int n, int d) {
    return (2 * a1 + d * (n - 1)) * n / 2;
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    int n, m;
    cin >> n >> m;
    string a, b;
    cin >> a >> b;
    map<int, int> cnt, kol;
    for (int i = 0; i < m; ++i) {
        ++cnt[b[i]];
    }
    int ans = 0, l = 0;
    for (int r = 0; r < n; ++r) {
        ++kol[a[r]];
        while (kol[a[r]] > cnt[a[r]] && l <= r) {
            --kol[a[l]];
            ++l;
        }
        ans += r - l + 1;
    }
    cout << ans << '\n';
}