# include <stdio.h>

const long int MAXL=10010;

char s[MAXL+1];

long long sol;long int n;
long int count[MAXL+1][27];

void citire()
{
     FILE *f=fopen("litere.in","r");
     fscanf(f,"%ld",&n);
     fgets(s+1,MAXL,f);
     fgets(s+1,MAXL,f);
     fclose(f);
}

void calculeaza()
{
     long int i,j;
     for (i=1;i<=n;i++)
         {
         for (j=1;j<=26;j++)
             count[i][j]=count[i-1][j];
         for (j=1;j<=s[i]-'a';j++)
             count[i][j]++;
         }
     for (i=1;i<=n;i++)
         sol+=count[i][s[i]-'a'+1];
}

void scrie()
{
     FILE *g=fopen("litere.out","w");
     fprintf(g,"%lld\n",sol);
     fclose(g);
}

int main()
{
    citire();
    calculeaza();
    scrie();
    return 0;
}