DateTime.class_eval do
  def russian_holiday?
    all_russian_holidays = [
        DateTime.new(2015, 1, 1),
        DateTime.new(2015, 1, 2),
        DateTime.new(2015, 1, 5),
        DateTime.new(2015, 1, 6),
        DateTime.new(2015, 1, 7),
        DateTime.new(2015, 1, 8),
        DateTime.new(2015, 1, 9),
        DateTime.new(2015, 2, 23),
        DateTime.new(2015, 3, 9),
        DateTime.new(2015, 5, 1),
        DateTime.new(2015, 5, 4),
        DateTime.new(2015, 5, 11),
        DateTime.new(2015, 6, 12),
        DateTime.new(2015, 11, 4)
    ]
    if all_russian_holidays.index(self).nil?
      false
    else
      true
    end
  end
end