#include "bits/stdc++.h"
using namespace std;

#define REP(i, n) for (int i = 0; i < n; i++)
#define ll long long

ll n, ans = 0;
string s;
void solve(ll i, string t){
  if(t.size() == 5){
    set<char> se;
    REP(i, 5) se.insert(t[i]);
    if(se.size() == 4 and t[0] == t[2])ans++;
    return;
  }
  if(i == n) return;
  solve(i + 1, t);
  solve(i + 1, t + s[i]);
}
int main(){
  cin >> n >> s;
  solve(0, "");
  cout << ans << endl;
}