#!/usr/bin/perl
use strict;
use warnings;

while (1) {
print "Type a number between 1000-9999:";
chomp (my $num=<STDIN>);
redo if $num !~ /^\d\d\d\d$/;
redo if $num =~ /^(\d)\1\1\1$/;

until ($num==6174) {
	my @big_to_small=sort {$b <=> $a } split //,$num;
	my @small_to_big=reverse @big_to_small;
	my $left=join "",@big_to_small;
	my $right=join "",@small_to_big;
	$num=scalar($left-$right);
	print "$left-$right=","$num\n";
 }
print "-" x 15,"\n";
}
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