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

my %chain;
# read the chain:
while (<DATA>){
	chomp;
	my ($key, $val) = split m/ \| /;
	push @{$chain{$key}}, $val;
}



# walk the chain starting from 12:

walk(12);

sub walk {
	my $c = shift;
	print "Visiting $c\n";

	for (@{$chain{$c}}){
		walk($_);
	}
}



__DATA__
23 | 32
12 | 45
12 | 35
12 | 67
45 | 34
34 | 90
34 | 55
35 | 53
35 | 44
44 | 41