#include<stdio.h>
int main()
{
char aux;
long n,num,i,es;
char s[10002];


  freopen("litere.in","r",stdin);
  freopen("litere.out","w",stdout);

  scanf ("%ld ",&n);
  gets(s);

  num=0;
   do
    {
      es=1;
      for (i=0;i<n-1;i++)
	if (s[i]>s[i+1])
	 {
	   aux=s[i];
	   s[i]=s[i+1];
	   s[i+1]=aux;
	   es=0;
	   num++;

	 }

    }while(es==0);


   printf("%ld",num);

return 0;
}