#!/usr/bin/perl

use strict;
use warnings 'all';

my (%data, @data, $data);

while (<DATA>) {
    chomp;
    push @{$data {$_}} => $_;
}

@data = @data {sort {$a <=> $b} keys %data};

while (@data) {
    $data = shift @data;
    print pop @$data, "\n";
    push @data => $data if @$data;
}

__DATA__
2
2
2
3
3
3
4
4
4