class RocketEquation
  attr_reader :mass
  def initialize(mass)
    @mass = mass
  end

  def self.for(line)
    new line.to_i
  end

  def fuel_required
    [(mass / 3) - 2, 0].max
  end

  def more_fuel_required
    return 0 unless mass.positive?

    fuel_required + RocketEquation.new(fuel_required).more_fuel_required
  end
end