#include<fstream>
#include<string.h>
#define MAX 10000

using namespace std;

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

void citire(int &n,char c[MAX])
{
     fin>>n;
     fin>>c;
}
void permmin(int n,char c[MAX])
{
     int p = 0,sort = 0,i;
     char aux;
     //fout<<c;
     while(!sort)
     {
         sort = 1;
         for(i = 0; i < n-1; i++)
         if(c[i] > c[i+1])
         {
             //        fout<<c[i]<<" "<<c[i+1]<<"\n";
                      aux  = c[i];
                      c[i] = c[i+1];
                      c[i+1] = aux;
                      sort = 0;
                      p++;
                      break;
         }
     }
fout<<p;
//fout<<c;
}
int main()
{
    char c[MAX];
    int n;
    citire(n,c);
    permmin(n,c);

fin.close();
fout.close();

return 0;
}