def get_real_mac(sentence):
    # Here, I assume that MAC address is seperated by a colon, or by a dash, but not by both.
    colon_pattern = r'[0-9abcde]{2}:[0-9ABCDEF]{2}:[0-9ABCDEF]{2}:[0-9ABCDEF]{2}:[0-9ABCDEF]{2}:[0-9ABCDEF]{2}'
    colon_matches = re.findall(colon_pattern, sentence, re.IGNORECASE)

    dash_pattern = re.sub(r':', r'-', colon_pattern)
    dash_matches = re.findall(dash_pattern, sentence, re.IGNORECASE)

    rt_list = colon_matches + dash_matches
    if rt_list:
        return rt_list[0]
    return None