input: def get_current_datetime() -> str:
      """ Get the current date and time and return it as a string in the format of YYYY-MM-DD HH:MM:SS.
      >>> get_current_datetime()
      '2023-10-05 14:30:45'
      """
output:     from datetime import datetime
      return datetime.now().strftime('%Y-%m-%d %H:%M:%S')