#include <bits/stdc++.h>

int main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  int n;
  std::string s;
  std::cin >> n >> s;
  int ans = 0;
  for (int a = 0; a < n; a++) {
    for (int b = a + 1; b < n; b++) {
      for (int c = b + 1; c < n; c++) {
        for (int d = c + 1; d < n; d++) {
          for (int e = d + 1; e < n; e++) {
            if (s[a] != s[c]) {
              continue;
            }
            if (s[a] == s[b] || s[a] == s[d] || s[a] == s[e]) {
              continue;
            }
            if (s[b] == s[c] || s[b] == s[d] || s[b] == s[e]) {
              continue;
            }
            if (s[c] == s[d] || s[c] == s[e]) {
              continue;
            }
            if (s[d] == s[e]) {
              continue;
            }
            ans++;
          }
        }
      }
    }
  }
  std::cout << ans << '\n';
}