# Pastebin bjEhb1sU
def is_prime(x)
    if x < 2  
		return false
	end
    if x == 2 
		return true
	end
	(2..Math.sqrt(x).sqrt.ceil + 1).each do |i|
        if x % i == 0
			return false
		end
	end
    true
end

num = 600851475143
max = 0;

i = 2;
    while i <= num 
        if num % i == 0 && is_prime(i) 
            puts "#{i} is a prime factor"
            num /= i;
            if i > max 
				max = i
			end
            i = 2;
		end

        i += 1
	end

    puts "Largest prime factor: #{max}"