#include <iostream>
#include <fstream>
using namespace std;
int fr[30];
char s[10001];
int main()
{
	ifstream in("litere.in");
	ofstream out("litere.out");
	int n, x;
	int ma = 0;
	int frmax = 0;
	cin >> n;
	int ma = 0;
	for (int i = 0;i < n;i++) {
		cin >> s[i];
		fr[s[i] - 'a']++;
		ma = max(ma, int(s[i] - 'a'));
	}
	int contor = 0;
	for (int i = 0;i < n - 1;i++) {
		int k = int(s[i] - 'a');
		fr[k]--;
		for (int j = 0;j <=ma;j++) {
			contor += fr[j];
		}
	}
	cout << contor;
}