#include <iostream>
#include <string>

int main() {
    int n;
    std::string s;
    std::cin >> n >> s;
    int ans = 0;
    auto rec = [&](auto self, int pos, std::string &t) -> void {
        const auto len = t.size();
        if (len == 5) {
            ans++;
            return;
        }

        for (int i = pos; i < n; i++) {
            if (len == 2) {
                if (s[i] == t[0]) {
                    t.push_back(s[i]);
                    self(self, i + 1, t);
                    t.pop_back();
                }
            } else {
                bool ng = false;
                for (const char c : t) {
                    ng |= (s[i] == c);
                }
                if (!ng) {
                    t.push_back(s[i]);
                    self(self, i + 1, t);
                    t.pop_back();
                }
            }
        }
    };
    std::string t;
    rec(rec, 0, t);
    std::cout << ans;
}