#include<fstream.h>
int main()
{
 int n,j,i,gasit,nr=0;
 char s[10001],aux;
 ifstream f("litere.in");
 ofstream g("litere.out");
 f>>n;
 f.get();
 f.get(s,n);
 gasit=1;
 while(gasit)
 { gasit=0;
  for(i=0;i<n-2;i++)
   if(i&& s[i]>s[i+1])
      {
      gasit=1;
       nr++;
       aux=s[i];
       s[i]=s[i+1];
       s[i+1]=aux;
     }
  }
  g<<nr;
 }