#include"fstream.h"
int main()
{
    ifstream fin("litere.in");
    ofstream fout("litere.out");
    
    int n,i,pp=1,q=0;
    char v[10010],aux;
    fin>>n;
    for(i=1;i<=n;i++)
       fin>>v[i];
    fin.close();
    while(pp)
    {
        pp=0;
        for(i=1;i<n;++i)
           if((int)v[i]>(int)v[i+1])
           {
               aux=v[i+1];
               v[i+1]=v[i];
               v[i]=aux;
               pp=1;
               q++;
           }
      }
    fout<<q;
    fout.close();
    return 0;
}