#define DMAX 11000
#include<stdio.h>
#include<string.h>
char s[DMAX];
int n,i,j,aux,ok,nr,x[DMAX];
int main()
{
 freopen("litere.in","r",stdin);
 freopen("litere.out","w",stdout);
 scanf("%ld\n",&n);
 gets(s);
 for(i=1;i<=n;i++)
  x[i]=s[i-1];
 do
 {
  ok=1;
  for(i=1;i<n;i++)
   {
    if(x[i]>x[i+1])
     {
      aux=x[i];
      x[i]=x[i+1];
      x[i+1]=aux;

      ok=0;
      nr++;
     }
   }
 }while(ok==0);
 printf("%ld",nr);
 fcloseall();
 return 0;
}