#include <iostream>
#include <fstream>

using namespace std;

ifstream fin ("litere.in");
ofstream fout ("litere.out");

int n, sol, ok;

char v[10001], aux;

int main (){

      fin>>n;

      for(int i=1; i<=n; i++)
            fin>>v[i];

      do{
            ok=0;
            for(int i=1; i<n; i++){
                  if((int)v[i] > (int)v[i+1]){
                        ok=1;
                        sol++;
                        aux=v[i];
                        v[i]=v[i+1];
                        v[i+1]=aux;
                  }
            }
      }while(ok != 0);

      fout<<sol;

      return 0;
}