import re


def check_mac(mac_address, capital_letters=True):
    """
    Check mac address is valid.
    Either format of 52:54:00:AE:E3:41, or
    52-54-00-AE-E3-41
    """
    if capital_letters:
        regex = r'^([0-9A-F]{2}[:]){5}([0-9A-F]{2})$'
    else:
        regex = r'^([0-9a-f]{2}[:]){5}([0-9a-f]{2})$'
    if (re.fullmatch(regex, mac_address)):
        return 0
    return -1