#include <stdio.h>
FILE *f=fopen("litere.in","r"),*g=fopen("litere.out","w");
long int n,v[30],i,j,sum=0,p;
char ch;

int main()
{
    fscanf(f,"%ld\n",&n);
    for(i=1; i<=n; i++){
        fscanf(f,"%c",&ch);
        p=ch-'a';
        v[p]++;
        for(j=p+1; j<=25; j++){
            sum+=v[j];
        }
    }
    fprintf(g,"%ld",sum);
    return 0;
}