#!/usr/bin/perl

use strict;

my $string;
while( <DATA> ) {
    $string = $string . join " ", split( /\:/ );
}

my $data = join "\n",
           map { $_->[0] }
           sort { $a->[1] <=> $b->[1] }
           map { [$_, (split)[0]] }
           split( /\n/, $string);

print $data;

__DATA__
2.225:0:1248266065752:Y:282
2.232:0:1248266069770:Y:500
2.225:1:1248266072861:Y:438
2.232:1:1248266075785:Y:328
2.225:1:1248266081283:Y:297
2.232:1:1248266082035:Y:328
2.232:1:1248266087410:Y:281
2.225:1:1248266088768:Y:296
2.232:1:1248266091426:Y:281