#include<stdio.h>
using namespace std;
int v[10001],n,i,j,nr,g[10001];
int main()
{
	char x;
	freopen("litere.in","r",stdin);
	freopen("litere.out","w",stdout);
    scanf("%d",&n);
	scanf("%c",&x);
    for(i=1;i<=n;i++)
    {
        scanf("%c",&x);
        v[x-96]++;
        for(j=x-96;j<=27;j++)
            nr+=v[j+1];
    }
    printf("%d",nr);
    return 0;
}