#!/usr/bin/perl -w
use strict;

my %host_seen = ();
my @hosts_sorted = ();

while (<>)
{
  chomp;
  my ($host, $url) = split;
  if ($host =~ /^[a-zA-Z]/)
  {
    # convert to reverse dot notation for symbolic host names
    $host = join(".", reverse split(/\./, $host));
  }
  $host_seen{$host}++;
}
{
  my $prev = '';
  @hosts_sorted = grep
		    {
		      if ($prev eq ''
		          || substr($_, 0, length($prev)) ne $prev)
		      {
		        my $host = $_;
		        $prev = $host;
		        if ($host =~ /^[a-zA-Z]/)
		        {
			  # reverse back to normal representation.
			  $host = join(".", reverse split(/\./, $host));
		        }
			print "$host\n";
		      }
		    } sort keys %host_seen;
}