#include <fstream.h>
char sir[10002];
long long n,S;
void citire()
{
   ifstream fin("litere.in");
   fin>>n;
   for (int i=0;i<n;i++ )
      fin>>sir[i];
   fin.close();
}

void numarare()
{
   for (int i=0;i<n;i++)
      for (int j=0;j<i;j++)
	 if (sir[j]>sir[i]){
	    S++;}
}

int main()
{
   citire();
   numarare();
   ofstream fout("litere.out");
   fout<<S;
   fout<<"\n";
   fout.close();
   return 0;
}