#include <fstream.h>
int main()
{
long n,i;char c2[10000];int c[10000],terminat,aux,nr=0;
ifstream f("litere.in");
f>>n;
for(i=0;i<n;i++)
   {f>>c2[i];
    c[i]=int(c2[i]);
   }
terminat=0;
while(!terminat)
  {
  terminat=1;
    for(i=0;i<n-1;i++)
      if(c[i]>c[i+1]) {aux=c[i];c[i]=c[i+1];c[i+1]=aux;terminat=0;nr++;}
  }
ofstream g("litere.out");
g<<nr;
return 0;
}