#include <bits/stdc++.h>
#include <atcoder/all>
#include <boost/multiprecision/cpp_dec_float.hpp>
#include <boost/multiprecision/cpp_int.hpp>
namespace mp = boost::multiprecision;
using Bint = mp::cpp_int;
using namespace std;
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
    int n;
    string s;
    cin >> n >> s;
    int ans = 0;
    auto dfs = [&](auto dfs, int u, string t) -> void {
        if(t.size()==5) {
            set<char> st;
            rep(i,5) st.insert(t[i]);
            if(t[0]==t[2] && st.size()==4) {
                ans++;
            }
            return;
        }
        for(int i=u;i<n;i++) {
            dfs(dfs, i+1, t+s[i]);
        }
    };
    dfs(dfs, 0, "");
    cout << ans << endl;
    return 0;
}