#include<stdio.h>
FILE *f=fopen("litere.in","r"),*g=fopen("litere.out","w");
char a;
unsigned long inv,n,alfabet[28];

int main()
{
    int i;
    fscanf(f,"%ld\n",&n);
    for(unsigned long k=1;k<=n;k++)
        {
        fscanf(f,"%c",&a);
        i=a-'a';
        for(int j=i+1;j<='z'-'a';j++)
            if(alfabet[j])
                inv+=alfabet[j];
        alfabet[i]++;
        }
    fprintf(g,"%ld",inv);
    fclose(f);
    fclose(g);
return 0;
}