class Screen(object):

    @property

    def width(self):

        return self.__width

    @property

    def height(self):

        return self.__height

    @width.setter

    def width(self,value):

        if not isinstance(value,int):

            raise ValueError('must be integer!')

        if value<0:

            raise ValueError('must bigger than 0!')

        self.__width=value

    @height.setter

    def height(self,value):

        if not isinstance(value,int):

            raise ValueError('must be integer!')

        if value<0:

            raise ValueError('must bigger than 0!')

        self.__height=value

    @property

    def resolution(self):

        self.__resolution=self.__width*self.__height

        return self.__resolution