#include <stdio.h>

long i, n, sch;
char l[10001];

FILE *fin, *fout;

void bubblesort(void)
{
  int s;
  char aux;

  sch = 0;
  do
   {
    s = 0;
    for (i = 0; i<n-1; i++)
      if (l[i]>l[i+1])
        {
          sch++;
          s = 1;
          aux = l[i];
          l[i] = l[i+1];
          l[i+1] = aux;
        }
   }while(s);
}

int main(void)
{
  fin = fopen("litere.in", "r");
  fout = fopen("litere.out", "w");
  fscanf(fin, "%ld\n", &n);
  fscanf(fin, "%s", &l);
  bubblesort();
  fprintf(fout, "%ld\n", sch);
  fclose(fout);
  return 0;
}