#include <stdio.h>
#define N 10128
char v;
int f[150];
int main()
{
	int i,j,n,rez=0;
	freopen("litere.in", "r",stdin);
	freopen("litere.out", "w",stdout);
	scanf("%d", &n);
	for(i=0;i<=n;++i)
	{
		scanf("%c", &v);
		for(j=v;j>=96;--j,++f[j]);
		rez+=f[v];
	}	
	printf("%d\n", rez);
	return 0;
}