input:     
  def str_to_lower(string: str) -> str:
      """
      Converts a given string to its lowercase version.
  
      >>> str_to_lower("HELLO World")
      'hello world'
      >>> str_to_lower("Python PROGRAM")
      'python program'
      >>> str_to_lower("12345ABC!@#")
      '12345abc!@#'
      """
output:     return string.lower()