#include<stdio.h>

int n,i,j,aux,s,min,poz,k;
int v[100];

int main(){
 FILE*f=fopen("litere.in","r");
 FILE*g=fopen("litere.out","w");
  fscanf(f,"%d\n",&n);
  for(i=1;i<=n;i++)
    fscanf(f,"%c",&v[i]);
 for(k=1;k<=n;k++)
  for(i=1;i<n;i++)
	 if(v[i]>v[i+1]){
	   aux=v[i];
	   v[i]=v[i+1];
	   v[i+1]=aux;
	   s++;
   }

/*  for(i=1;i<n;i++){
   min=v[i];
   poz=i;
   for(j=i+1;j<=n;j++){
	 if(min>v[j]){
	 min=v[j];
	 poz=j;

	 }

   }
   aux=v[i];
   v[i]=v[poz];
   v[poz]=aux;

 } */
 // for(i=1;i<=n;i++)
   // fprintf(g,"%c",v[i]);
   fprintf(g,"%d",s);
 fclose(f);
 fclose(g);
 return 0;
}