#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int n;
  string s;
  cin >> n >> s;
  int ans = 0;
  for (int i = 0; i < n; ++i) {
    for (int j = i + 1; j < n; ++j) {
      for (int k = j + 1; k < n; ++k) {
        for (int l = k + 1; l < n; ++l) {
          for (int m = l + 1; m < n; ++m) {
            set<char> st = { s[i], s[j], s[k], s[l], s[m] };
            if (st.size() == 4 && s[i] == s[k]) ++ans;
          }
        }
      }
    }
  }
  cout << ans << '\n';
  return 0;
}