#!/usr/bin/perl

use strict;
use warnings;

my @lines   = ();
my %numbers = ();

while(<DATA>) {
    my ($number) = m/^(\d+)/;

    push @lines, [$number, $_];
    $numbers{$number}++;
}

foreach (@lines) {
    print $_->[1] if $numbers{$_->[0]} > 1;
}

__DATA__
1  ahjewgfje
1  gopjregre
2  kkkkkkk
3  figjiorger
3  rekopfroeer
3  ejfjviknced
4  erjgirjgerio
5  eieuiee
5  reopjtfrpeoi