#include <iostream>
#include <fstream>

using namespace std;

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

int main(){
   int n;
   string s;
   fin >> n >> s;
   int csere=1, vege=n-1, cnt=0;
   while(csere!=-1){
      csere=-1;
      for(int i=0; i<vege; i++){
         if(s[i]>s[i+1]){
            swap(s[i], s[i+1]);
            cnt++;
            csere=i;
         }
      }
      vege=csere;
   } 
   fout << cnt;
   return 0;
}