code: def is_valid_ymd(year, month, day):
      
  
      return 1 <= month <= 12 and 1 <= day <= days_in_month(year, month) and year >= 1899
docs: return True if (year,month, day) can be represented in Excel-notation
      (number of days since 30.12.1899) for calendar days, otherwise False
  
      :param int year: calendar year
      :param int month: calendar month
      :param int day: calendar day
      :return bool: