#include <iostream>
#include <fstream>

using namespace std;

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

int n, sol;

char v[10001];

int main (){

      fin>>n;

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

            for(int j=i-1; j>=1; j--){
                  if((int)v[i] < (int)v[j])
                        sol++;
            }
      }

      fout<<sol;

      return 0;
}