class Screen(object):

    @property

    def width(self):

        return self._width

    @width.setter

    def width(self, value):

        if not isinstance(value, (int, float)) and value > 0:

            raise ValueError('Please input right number!')

        else:

            self._width = value 

    @property

    def height(self):

        return self._height

    @height.setter

    def height(self, value):

        if not isinstance(value, (int, float)) and value > 0:

            raise ValueError('Please input right number!')

        else:

            self._height = value 

    @property

    def resolution(self):

        self._resloution = self._height * self._width

        return self._resloution