#include<stdio.h>
int i,n,sortat;
long nr;
char aux,v[10001];
int main()
{
freopen("litere.in","r",stdin);
freopen("litere.out","w",stdout);
scanf("%d\n",&n);
for(i=1;i<=n;i++)
  scanf("%c",&v[i]);
do
  {
  sortat=1;
  for(i=1;i<n;i++)
    if(v[i]>v[i+1])
      {
      aux=v[i];
      v[i]=v[i+1];
      v[i+1]=aux;
      nr++;
      sortat=0;
      }
  }while(!sortat);
printf("%ld",nr);
return 0;
}