def response_formatter(text, username, max_length=140):
    """
    Formats response to be below ``max_length`` characters long.

    Args:
        text (str): text to return
        username (str): username to @. @<username> is tacked on to end of tweet
        max_lenght (int): max length of tweet. Default: ``140``

    Returns:
        (str): the tweet text
    """
    while len('{} @{}'.format(text, username)) > max_length:
        text = text[:-1]

    return '{} @{}'.format(text, username)