#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
typedef long long ll;
const int INF = 1<<30;
const ll INFLL = 1LL<<60;
const ll MOD = 1000000007;
const double INFD = 1.0E10;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, -1, 0, 1};
//const int dx[8] = {1, 1, 0, -1, -1, -1, 0, 1};
//const int dy[8] = {0, 1, 1, 1, 0, -1, -1, -1};
using Pair = pair<ll, ll>;
using Graph = vector<vector<ll, ll> >;
using mint = atcoder::modint1000000007;


int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(15);
    int n; cin >> n;
    string s; cin >> s;
    int ans = 0;
    for (int i = 0; i < n - 4; i++){
        for (int j = i + 1; j < n - 3; j++){
            for (int k = j + 1; k < n - 2; k++){
                for (int l = k + 1; l < n - 1; l++){
                    for (int m = l + 1; m < n; m++){
                        if (s[i] != s[k]) continue;
                        vector<int> vec = {s[i], s[j], s[k], s[l], s[m]};
                        sort(vec.begin(), vec.end());
                        vec.erase(unique(vec.begin(), vec.end()), vec.end());
                        if (vec.size() != 4) continue;
                        ans++;
                    }
                }
            }
        }
    }
    
    
    cout << ans << endl;
    
    return 0;
}