def count_happy_day_in_2015
  last_day_of_month = [31,28,31,30,31,30,31,31,30,31,30,31]
  counter = 0
  1.upto(12) do |month|
    0.upto(month) do |upper_digit|
      lower_digit = month - upper_digit

      break if upper_digit * 10 + lower_digit > last_day_of_month[month-1]

      if (0..9).include?(lower_digit)
        counter += 1
      end
    end
  end
  counter
end

p count_happy_day_in_2015