#include <bits/stdc++.h>

using namespace std;

typedef pair<int, int> pii;
typedef pair<int, pair<int, int> > piii;
typedef long long ll;
const int N = 2000086, MOD = 1e9 + 7, INF = 0x3f3f3f3f;
ll res;
int n, m, cnt, w[N];

char s[N];

int main() {
    cin >> n;
    scanf("%s", s + 1);
    for (int i = 1; i < n + 1; i++)
        for (int j = i + 1; j < n + 1; j++)
            if (s[i] != s[j])
            for (int k = j + 1; k < n + 1; k++)
                if (s[i] == s[k])
                for (int l = k + 1; l < n + 1; l++)
                    for (int o = l + 1; o < n + 1; o++) {
                        set<char> st = {s[i], s[j], s[l], s[o]};
                        res += st.size() == 4;
                    }
    printf("%lld\n", res);
    return 0;
}