def to_24_hour_clock(hours):
    """ (number) -> number

    hours is a number of hours since midnight. Return the
    hour as seen on a 24-hour clock.

    Precondition: hours >= 0

    >>> to_24_hour_clock(24)
    0
    >>> to_24_hour_clock(48)
    0
    >>> to_24_hour_clock(25)
    1
    >>> to_24_hour_clock(4)
    4
    >>> to_24_hour_clock(28.5)
    4.5
    """

    return hours % 24