#!/usr/bin/env perl

use strict;
use warnings;

use List::Util qw(all);

my $n = 600851475143;

# Functional

# Imperative
my @primes;
my $last_factor;

for my $i (2 .. $n) {
	if ($i > $n) {
		last;
	}
	if (all { $i % $_ != 0 } @primes) {
		push(@primes, $i);
		if ($n % $i== 0) {
			$n = $n / $i;
			$last_factor = $i;
			redo;
		}
	}
}
print "$last_factor\n";