input: def str_to_lower(string: str) -> str:
      """Convert a given string to its lowercase version.
      >>> str_to_lower("Hello World")
      'hello world'
      >>> str_to_lower("PYTHON IS GREAT")
      'python is great'
      >>> str_to_lower("12345!@#$%")
      '12345!@#$%'
      """
output:     return string.lower()