#include<fstream>
#define MAX 10000

using namespace std;

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

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

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

return 0;
}