#include <bits/stdc++.h>

using namespace std;
using ll = long long;
// --------------------------------------------------------
template <class T>
bool chmax(T &a, const T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
bool chmin(T &a, const T b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
#define FOR(i, l, r) for (ll i = (l); i < (r); ++i)
#define RFOR(i, l, r) for (ll i = (r) - 1; (l) <= i; --i)
#define REP(i, n) FOR(i, 0, n)
#define RREP(i, n) RFOR(i, 0, n)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define SORT(c) sort(ALL(c))
#define RSORT(c) sort(RALL(c))
#define MIN(c) *min_element(ALL(c))
#define MAX(c) *max_element(ALL(c))
#define SUM(c) accumulate(ALL(c), 0LL)
#define BITCNT(c) __builtin_popcountll(c)
#define SZ(c) ((int)(c).size())
#define COUT(c) cout << (c) << '\n'
#define debug(x) cerr << #x << " = " << (x) << '\n';
using P = pair<ll, ll>;
using VP = vector<P>;
using VVP = vector<VP>;
using VS = vector<string>;
using VI = vector<int>;
using VVI = vector<VI>;
using VLL = vector<ll>;
using VVLL = vector<VLL>;
using VB = vector<bool>;
using VVB = vector<VB>;
using VD = vector<double>;
using VVD = vector<VD>;
static const double EPS = 1e-10;
static const double PI = acos(-1.0);
template <typename T>
void arrPrint(vector<T> arr) {
  for (auto v : arr) cout << v << " ";
  cout << '\n';
}
template <typename T>
void arrPrint2Dim(vector<vector<T>> arr) {
  for (auto a : arr) arrPrint(a);
}
template <typename T, typename T2>
void arrPrintPair(vector<pair<T, T2>> arr) {
  for (auto v : arr) cout << "{" << v.first << "," << v.second << "}, ";
  cout << '\n';
}
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }

// static const int INF = (1 << 30) - 1;  // 1073741824 - 1
static const ll INF = (1LL << 62) - 1;  // 4611686018427387904 - 1
// static const ll MOD = 1000000007;
static const ll MOD = 998244353;

int main() {
  ll N;
  cin >> N;
  string S;
  cin >> S;
  ll ans = 0;
  auto dfs = [&](auto &&dfs, ll idx, string str) {
    if (idx == N) return;
    if (SZ(str) == 5) {
      if (str[0] != str[2]) return;
      set<char> st;
      for (auto c : str) st.insert(c);
      if (SZ(st) != 4) return;
      ans++;
      return;
    }
    FOR(i, idx + 1, N) {
      str.push_back(S[i]);
      dfs(dfs, i, str);
      str.pop_back();
    }
  };
  dfs(dfs, -1, "");
  cout << ans << '\n';
}