#include <bits/stdc++.h>

#define REP_OVERLOAD(arg1, arg2, arg3, arg4, NAME, ...) NAME
#define REP3(i, l, r, s)                                               \
    for (int i = int(l), rep3_r = int(r), rep3_s = int(s); i < rep3_r; \
         i += rep3_s)
#define REP2(i, l, r) REP3(i, l, r, 1)
#define REP1(i, n) REP2(i, 0, n)
#define rep(...) REP_OVERLOAD(__VA_ARGS__, REP3, REP2, REP1, )(__VA_ARGS__)
#define repin(i, l, r) for (int i = int(l), repin_r = int(r); i <= repin_r; ++i)

#define RREP_OVERLOAD(arg1, arg2, arg3, arg4, NAME, ...) NAME
#define RREP3(i, l, r, s)                                                      \
    for (int i = int(r) - 1, rrep3_l = int(l), rrep3_s = int(s); i >= rrep3_l; \
         i -= rrep3_s)
#define RREP2(i, l, r) RREP3(i, l, r, 1)
#define RREP1(i, n) RREP2(i, 0, n)
#define rrep(...) RREP_OVERLOAD(__VA_ARGS__, RREP3, RREP2, RREP1, )(__VA_ARGS__)
#define rrepin(i, l, r) \
    for (int i = int(r), rrepin_l = int(l); i >= rrepin_l; --i)

#define all(v) v.begin(), v.end()


#include <algorithm>
#include <cassert>
#include <iostream>
#include <vector>

namespace rklib {

template <class T>
std::ostream &operator<<(std::ostream &os, const std::vector<T> &v) {
    os << "[";
    for (auto d : v) os << d << ", ";
    return os << "]";
}

// a <- max(a, b)
template <class T>
bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

// a <- min(a, b)
template <class T>
bool chmin(T &a, const T &b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}

// if a < 0: a <- b
// else: a <- min(a, b)
template <class T>
bool chmin_non_negative(T &a, const T &b) {
    if (a < 0 || a > b) {
        a = b;
        return true;
    }
    return false;
}

// floor(num / den)
template <class T>
T div_floor(T num, T den) {
    if (den < 0) num = -num, den = -den;
    return num >= 0 ? num / den : (num + 1) / den - 1;
}

// ceil(num / den)
template <class T>
T div_ceil(T num, T den) {
    if (den < 0) num = -num, den = -den;
    return num <= 0 ? num / den : (num - 1) / den + 1;
}

}  // namespace rklib


using namespace std;
using namespace rklib;

using lint = long long;
using ulint = unsigned long long;
using pii = pair<int, int>;
using pll = pair<lint, lint>;
template <class T>
using vec = vector<T>;
template <class T>
using vvec = vec<vec<T>>;
template <class T>
using vvvec = vec<vvec<T>>;

lint count(string &s, string &t) {
    int n = s.size();
    vvec<lint> dp(n + 1, vec<lint>(6, 0));
    dp[0][0] = 1;
    rep(i, n) rep(j, 6) {
        if (dp[i][j] > 0) {
            dp[i + 1][j] += dp[i][j];
            if (j < 5 && s[i] == t[j]) {
                dp[i + 1][j + 1] += dp[i][j];
            }
        }
    }
    return dp[n][5];
}

int main() {
    int n;
    string s;
    cin >> n >> s;

    lint ans = 0;
    rep(i, 26) {
        rep(j, 26) {
            rep(k, 26) {
                rep(l, 26) {
                    set<int> S = {i, j, k, l};
                    if (S.size() < 4) {
                        continue;
                    }

                    string t;
                    t += 'A' + i;
                    t += 'A' + j;
                    t += 'A' + i;
                    t += 'A' + k;
                    t += 'A' + l;
                    ans += count(s, t);
                }
            }
        }
    }
    cout << ans << "\n";
}