#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, t) for (ll i = s; i < (ll)(t); i++)
#define all(x) begin(x), end(x)

template <typename T> bool chmin(T& x, T y) {
	return x > y ? (x = y, true) : false;
}
template <typename T> bool chmax(T& x, T y) {
	return x < y ? (x = y, true) : false;
}

struct IOST {
	IOST() {
		ios::sync_with_stdio(false);
		cin.tie(nullptr);
		cout << fixed << setprecision(20);
	}
} IOST;

void solve() {
	int n;
	cin >> n;
	string s;
	cin >> s;
	int ans = 0;
	rep(i0, 0, n) rep(i1, i0 + 1, n) rep(i2, i1 + 1, n) {
		if (s[i0] == s[i1]) break;
		if (s[i0] != s[i2]) continue;
		set<char> st = {s[i0], s[i1]};
		rep(i3, i2 + 1, n) rep(i4, i3 + 1, n) {
			if (s[i3] == s[i4]) continue;
			if (st.count(s[i3]) || st.count(s[i4])) continue;
			ans++;
		}
	}
	cout << ans << "\n";
}

int main() {
	int t = 1;
	// cin >> t;
	rep(i, 0, t) solve();
}