#!/usr/bin/perl

use strict;
use warnings;

exit unless @ARGV;

my %cache = do {local @ARGV = shift @ARGV; map {($_, 1)} <>};

while (@ARGV) {
    local @ARGV = shift @ARGV;
    %cache = map {$cache{$_} ? ($_, 1) : ()} <>;
}

print for keys %cache;

__END__