#include <bits/stdc++.h>
using namespace std;

#define For(i, a, b) for(int i = (a); i < (b); i++)
#define rep(i, n) For(i, 0, n)
#define rFor(i, a, b) for(int i = (a); i >= (b); i--)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()
#define SZ(v) ((int)(v).size())

using lint = long long;
using ld = long double;

int INF = 2000000000;
lint LINF = 1000000000000000000;

struct SetupIo {
    SetupIo() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
        cout << fixed << setprecision(15);
        cerr << fixed << setprecision(15);
    }
} setupio;

int main() {
    int n;
    string s;
    cin >> n >> s;
    vector<vector<int>> v(26);
    rep(i, n) {
        v[s[i] - 'A'].emplace_back(i);
    }
    int ans = 0;
    rep(A, 26) {
        rep(i, SZ(v[A])) {
            For(j, i + 1, SZ(v[A])) {
                int a1 = v[A][i], a2 = v[A][j];
                int cur = 1;
                rep(B, 26) {
                    if (A == B) { continue; }
                    rep(ii, SZ(v[B])) {
                        int b = v[B][ii];
                        if (!(a1 < b && b < a2)) { continue; }
                        rep(C, 26) {
                            if (A == C || B == C) { continue; }
                            rep(iii, SZ(v[C])) {
                                int c = v[C][iii];
                                if (!(a2 < c)) { continue; }
                                rep(D, 26) {
                                    if (A == D || B == D || C == D) { continue; }
                                    int l = upper_bound(ALL(v[D]), c) - v[D].begin();
                                    int r = SZ(v[D]);
                                    ans += r - l;
                                }
                            }
                        }
                    }
                }
            }
        }
    }
    cout << ans << "\n";
}