def rcumode2nyquistzone(rcumode):
    """\
    Compute Nyquist zone for given RCU mode.

    Parameters
    ----------
    rcumode: int or str
        The RCU mode (a.k.a SPW).

    Returns
    -------
    nqzone: int
        Nyquist zone number.
    """
    nqzone = int((int(rcumode)-3)/2)
    return nqzone