#include<iostream>
#include<string>
#include<set>
using namespace std;
using ll = long long;
int main() {
	int n;
	string s;
	cin >> n >> s;
	ll ans = 0;
	for (int i = 0; i < n; i++) {
		for (int j = i + 1; j < n; j++) {
			for (int k = j + 1; k < n; k++) {
				for (int l = k + 1; l < n; l++) {
					for (int m = l + 1; m < n; m++) {
						set<char>S;
						S.insert(s[i]);
						S.insert(s[j]);
						S.insert(s[k]);
						S.insert(s[l]);
						S.insert(s[m]);
						if (S.size() == 4 && s[i] == s[k])ans++;
					}
				}
			}
		}
	}
	cout << ans << endl;
}