#include <stdio.h>
#include <string.h>
char v[10000], aux, enter[2];
int sw, k, n;
int main(void)
{
 freopen("litere.in","r",stdin);
 freopen("litere.out","w",stdout);
 scanf("%d",&n);
 gets(enter);
 gets(v);
 do
 {
  sw = 1;
  for(register int i = 0; i < strlen(v)-1; i++)
   if(v[i] > v[i+1])
	{
	 k++;
	 aux = v[i];
	 v[i] = v[i+1];
	 v[i+1] = aux;
	 sw = 0;
	}
 }while(!sw);

 printf("%d",k);
 fcloseall();
 return 0;

}