#include <bits/stdc++.h>

#include <atcoder/all>
using namespace std;
using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
#define FAST_IO                \
  ios::sync_with_stdio(false); \
  cin.tie(0);
const i64 INF = 1001001001001001001;
using Modint = atcoder::static_modint<998244353>;

int dfs(int d, int i, string &S, vector<char> &a) {
  if (d == a.size()) {
    set<char> st;
    for (int j = 0; j < a.size(); j++) {
      st.insert(a[j]);
    }
    if (a[0] == a[2] && st.size() == 4) {
      return 1;
    }
    return 0;
  }

  int ans = 0;

  for (int j = i; j < S.size(); j++) {
    a[d] = S[j];
    ans += dfs(d + 1, j + 1, S, a);
  }

  return ans;
}


int main() {
  FAST_IO
  auto ans = 0LL;

  int N;
  cin >> N;
  string S;
  cin >> S;

  vector<char> a(5);
  ans = dfs(0, 0, S, a);

  cout << ans << endl;
}