#include<fstream.h>
ifstream f("litere.in");
ofstream g("litere.out");
char c;
unsigned int N;
unsigned long v[400],j,k,l,sw,aux,n,i;
int main()
{
f>>n;
for (i=1;i<=n;i++)
{
 f>>c;
 v[i]=c;
 }
l=1;
do
{
sw=0;
for(j=1;j<=n-l;j++)
 if(v[j]<v[j+1])
  {
  aux=v[j];
  v[j]=v[j+1];
  v[j+1]=aux;
  sw=1;
  l++;
  k=k+1;
  }
}while(sw==1);
g<<k;
f.close();
g.close();
return 0;
}