#include <bits/stdc++.h>
using namespace std;
//#include<atcoder/all>
//using namespace atcoder;
using ll = long long int;
using ull = unsigned long long int;
using ld = long double;
constexpr ll MAX = 2000000000000000000;
constexpr ld PI = 3.14159265358979;
constexpr ll MOD = 0;//2024948111;
ld dotorad(ld K){ return PI * K / 180.0; }
ld radtodo(ld K){ return K * 180.0 / PI; }
mt19937 mt;
void randinit(){ srand((unsigned)time(NULL));mt = mt19937(rand()); }
int main(){
    ll N;
    cin >> N;
    string S;
    cin >> S;
    ll ans = 0;
    for(ll i = 0;i < N;i++){
        for(ll j = i + 1;j < N;j++){
            for(ll k = j + 1;k < N;k++){
                for(ll l = k + 1;l < N;l++){
                    for(ll m = l + 1;m < N;m++){
                        if(S[i] == S[k]){
                            set<ll> st;
                            st.insert(S[i]);
                            st.insert(S[j]);
                            st.insert(S[l]);
                            st.insert(S[m]);
                            if(st.size() == 4){
                                ans++;
                            }
                        }
                    }
                }
            }
        }
    }
    cout << ans << endl;
}