#include <stdio.h>
#define input "litere.in"
#define output "litere.out"
#define DIM 10001
int main ()
{
    freopen (input, "r", stdin);
    freopen (output, "w", stdout);
    int n,i,j,k=0,o;
    char a[DIM],ch;
    scanf ("%d",&n);
    if (n==1)
    {
             scanf ("%c",&a[1]);
             printf ("0");return 0;
    }
    scanf ("%c",&ch);
    for (i=0; i<n; ++i)
        scanf ("%c",&a[i]);
    do
       {
              o=1;
              for (i=0;i<n-1;++i)
              {
                  if (a[i]>a[i+1])
                  {
                              o=0;
                              a[i]^=a[i+1];
                              a[i+1]^=a[i];
                              a[i]^=a[i+1];
                              k++;
                  }
              }
        }
	while (o==0);
    printf ("%d",k);
    return 0;
}