#!/usr/bin/perl
use strict;
use warnings;

print "Durchschnitt: ".(x(\(my $i=0)))[0]."\n";

sub x
{
  (local $_=<STDIN>) eq "\n" and return 0;
  (/^\d+/ && ++${$_[0]}) or die("NO NUMBER");
  return x($_[0])+($_/${$_[0]});
}