#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

void solve() {
  ll n;
  string s;
  cin >> n >> s;
  ll ans = 0;
  auto dfs = [&](auto self, vector<ll> &is) {
    if (is.size() == 5) {
      set<char> st;
      for (const auto i : is)
        st.insert(s[i]);
      if (st.size() == 4 && s[is[0]] == s[is[2]])
        ans++;
      return;
    }
    ll las = -1;
    if (!is.empty())
      las = is.back();
    for (ll i = las + 1; i < n; i++) {
      is.push_back(i);
      self(self, is);
      is.pop_back();
    }
  };
  vector<ll> is;
  dfs(dfs, is);
  cout << ans << '\n';
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}