def parse(address):
    """Parses the given MAC address and transforms it into "xx:xx:xx:xx:xx:xx"
    form. This form of expressing MAC addresses is the most standard one.
    In general, the "address" parameter accepts three forms of MAC address i
    input:
        - '1234567890af',
        - '12-34-56-78-90-af' (windows-like) and
        - '12:34:56:78:90:af' (the most used form).
    The 'address' parameter must be string, of course.
    """      
    assert address is not None
    temp = address
    if "-" in temp:
        temp = temp.replace("-", ":")
    if ":" not in temp:
        lst = list(temp)
        for cnt in range(10, 0, -2):
            lst.insert(cnt, ":")
        temp = ""
        for c in lst:
            temp = temp + c 
    return temp.lower()