#include <bits/stdc++.h>
using namespace std;
using lint = long long;
int main() {
  int n;
  string s;
  cin >> n >> s;
  vector<int> vec(n);
  for (int i = 0; i < n; i++) {
    vec[i] = s[i]-'A';
  }
  long long ans = 0;
  for (int i = 0; i < n; i++) {
    for (int j = i+1; j < n; j++) {
      if (vec[i] != vec[j]) continue;
      for (int k = i+1; k < j; k++) {
        if (vec[i] == vec[k]) continue;
        for (int a = j+1; a < n; a++) {
          if (vec[i] == vec[a] || vec[k] == vec[a]) continue;
          for (int b = a+1; b < n; b++) {
            if (vec[i] == vec[b] || vec[k] == vec[b] || vec[a] == vec[b]) continue;
            ans++;
          }
        }
      }
    }
  }
  cout << ans << endl;

}