#include<string.h>
#include<stdio.h>
int i,n,k,j;
FILE *f,*g;
char a[10000],c;
int main ()
{ f=fopen("litere.in","r");
  g=fopen("litere.out","w");
fscanf(f,"%d",&n);
fscanf(f,"%s",&a);
if(n%2==0&&n>=4)
for(i=0;i<n-1;i++)
    if(a[i]>a[i+1])
       k+=int(a[i])-int(a[i+1]);
    else
      k+=int(a[i+1])-int(a[i]);
else
for(i=0;i<n-1;i++)
 for(j=i+1;j<n;j++)
   if(a[i]>a[j])
    k++;
fprintf(g,"%d",k);
return 0;
}