#include <stdio.h>
#include <stdlib.h>
int main() {
	int n, sum, s2, i, j, a[27];
	char c, s[10001];

	freopen ("litere.in", "r", stdin);
	freopen ("litere.out", "w", stdout);

	scanf ("%d\n",&n);

	for (i = 1; i <= n; i++) {
		scanf ("%c",&c);
		s[i] = c;
	}
	sum = 0;
	for (i = 0; i <= 27; i++) a[i] = 0;
	for (i = 1; i <= n; i++) {
		s2 = 0;
		a[s[i]-'a'+1]++;
		for (j = s[i]-'a'+2; j<= 27; j++)
			s2 = s2 + a[j];
		sum = sum + s2;
	}

	printf ("%d",sum);


	return 0;

}