#include<stdio.h>
char s[10002];
int main()
{
long n,i,sortat,num=0;
char aux;

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

scanf("%ld\n",&n);
scanf("%s",&s);
do
  {
    sortat=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;
	     num++;
	     sortat=0;
	   }
   }while(sortat==0);
printf("%ld",num);
return 0;
}