#include <stdio.h>

FILE *f,*g;
int n,min,pmin,j,i,ok,contor=0;
char a[10000];

int main()
{
  f=fopen("litere.in","r");
  g=fopen("litere.out","w");
  fscanf(f,"%d\n",&n);
  fscanf(f,"%s\n",&a);
  for(i=0;i<=n-2;i++)
    {
      ok=0;
      min=a[i]; pmin=i;
      for(j=i+1;j<=n-1;j++)
	if(a[j]<min)
	  {
	    min=a[j];
	    ok=1;
	    pmin=j;
	  }
      a[pmin]=a[i];
      a[i]=min;
      if(ok!=NULL)contor++;

    }
  fprintf(g,"%d\n",contor);
  fclose(f);  fclose(g);
  return 0;
}