#include <stdio.h>
#include <string.h>

char *v;
int n;

long int x[130];
long int sum=0;
char c;

int main(){
  long int n,i,j;
  FILE *f = fopen("litere.in","r");
  fscanf(f,"%ld",&n);
  while ((c=fgetc(f))!='\n');
  v = new char[n+2];
  fscanf(f,"%s",v);
  fclose(f);
  for (i=0;i<strlen(v);i++) {
//    x[i]=0;
    for (j=v[i]+1;j<='z';j++) {
      sum+=x[j];
//      x[i]+=x[j];
    }
    x[v[i]]++;
  }

  delete v;


  FILE *g = fopen("litere.out","w");
  fprintf(g,"%ld",sum);
  fclose(g);
  return 0;
}