<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def save_downloaded_file(filename, save_file_at, file_stream):
 """ Save Downloaded File to Disk Helper Function :param save_file_at: Path of where to save the file. :param file_stream: File stream :param filename: Name to save the file. """

        filename = os.path.join(save_file_at, filename)
        with open(filename, 'wb') as f:
            f.write(file_stream)
            f.flush()