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

#define REP(i, n) for (int i = 0; i < n; i++)
#define REPR(i, n) for (int i = n; i >= 0; i--)
#define FOR(i, m, n) for (ll i = m; i < n; i++)
#define FORR(i, m, n) for (ll i = m; i >= n; i--)
#define REPO(i, n) for (ll i = 1; i <= n; i++)
#define ll long long
#define INF (ll)1ll << 60
#define MINF (-1 * INF)
#define ALL(n) n.begin(), n.end()
#define MOD (ll)1000000007
#define P pair<ll, ll>

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