def mbflow2str(flow: int):
    """unit of flow is MB
    """
    str = None
    if flow < 1024:
        return '%d Mb' % flow
    gb, mb = divmod(flow, 1024)
    if mb != 0:
        return '%d Gb %d Mb' % (gb, mb)
    else:
        return '%d Gb' % gb
