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

open my $f,"<","x.txt";
my %tree;
while (<$f>) {
  chomp;
  my ($c,$p)=split(/:/,$_);
  $tree{$c}=$p;
}
my %eert = reverse %tree;
foreach my $l (keys %tree) {
  if (!defined($eert{$l})) {
    my @g=($l);
    while($l) {
      $l=$tree{$l};
      push(@g,$l) if defined($l);
    }
    print join(':',@g),"\n";
  }
}