#include <stdio.h>
char v[10000],k;
int n,i,f,p,a;
FILE *in,*o;
main()
{
in=fopen("litere.in","r");
o=fopen("litere.out","w");
fscanf(in,"%d",&n);
for (i=0;i<=n;i++)
 {
 fscanf(in,"%c",&v[i]);
 for (f=1;f<i;f++)
  if (v[f]>v[i])
   p++;
 }
fprintf(o,"%d",p);
fclose(in);
fclose(o);
return 0;
}