#!/usr/bin/perl
use strict;
use warnings;
my $wantedLines = shift; # number of unique instances wanted

my $numFiles = 0;
my @files = ();
while( my $file = shift)
{
    open $files[$numFiles++], '<', $file or die "can't open $file, $!\n";
}

my $totalLines = 0;
my $ct = 0;
my %unique = ();

while($totalLines <= $wantedLines)
{
    my $num = $ct++;
    $num = $num%$numFiles;
    print "$num\n";

    my $this = <$files[$num]>;
    unless(exists $unique{$this})
    {
        print $this;
        $totalLines++;
    }
}