use strict;
use warnings;

my %pred;

while (<DATA>) {
	chomp;
	my @items = split /-/, $_;
	my $first = $items[0];
	for my $element (@items) {
		$pred{$element} = $first;
	}
}

print "$_ => $pred{$_}\n" for sort keys %pred;

__DATA__
123-234-345-456-567
117-228-339
131
213-324-435
372