def RR_calc(classes, TOP):
    """
    Calculate RR (Global performance index).

    :param classes: classes
    :type classes : list
    :param TOP: test outcome positive
    :type TOP : dict
    :return: RR as float
    """
    try:
        class_number = len(classes)
        result = sum(list(TOP.values()))
        return result / class_number
    except Exception:
        return 'None'
