#!/usr/bin/perl -w
use strict;

my $secret = shift;
until (length $secret == 1) {
	print "$secret\n";
	$secret = tpr($secret);
}
print "$secret\n";

sub tpr {
	my @digits = split //, shift;
	my $not_so_secret;
	while (my @pair = splice @digits, 0, 2) {
		unshift @digits, $pair[1]
			unless !@digits;
		my $res = $pair[0] + $pair[1];
		until ($res <= 9) {
			my $cpy = $res;
			$res = 0;
			for (split //, $cpy) {
				$res += $_;
			}
		}
		$not_so_secret .= $res;
	}
	return $not_so_secret;
}