class Calc0064
  def initialize(args)
    args = args.map { |l| l.chomp.split(/\s+/) }
    @f0, @f1, @n = args.shift.map(&:to_i)
  end

  def run
    fs = [@f0, @f1, @f0 ^ @f1]
    fs[@n % 3]
  end
end

puts Calc0064.new(STDIN.readlines).run if __FILE__ == $0