What will be the output of this Ruby code?

What will be the output of this Ruby code?

class Box
  include Comparable
  attr_reader :volume
  def initialize(volume)
    @volume = volume
  end
  def <=>(other)
    volume <=> other.volume
  end
end

box1 = Box.new(10)
box2 = Box.new(20)
puts box1 < box2