=begin

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 317584931803?

=end


def isPrime(i)
  print 'Prime? '+i.to_s+"\n"
  2.upto Math.sqrt(i).floor do |j|
    return false if (i % j) == 0
  end
  true
end

n = 317584931803
2.upto((n / 7).floor) do |i|
  qt = (n / i.to_f)
  if qt == qt.truncate && isPrime(qt)
    print qt.to_s
    exit
  end
end