#include<stdio.h>

char v[10000];
int a,n,i,j,nr;
char x;

int main(){
FILE *f=fopen("litere.in","r");

 fscanf(f,"%d\n",&n);

 for(i=1;i<=n;i++){
 fscanf(f,"%c",&v[i]);
 }

fclose(f);


nr=0;

a=n-1;

  for(j=1;j<=a;j++){

     for(i=1;i<=n-1;i++){

	if(v[i]>v[i+1]){

	x=v[i];
	v[i]=v[i+1];
	v[i+1]=x;
	nr++;
	}


     }
     n--;

  }


  FILE *g=fopen("litere.out","w");
  fprintf(g,"%d",nr);
  fclose(g);


return 0;
}