class Screen(object):

    @property

    def width(self):

        return self._width

    @width.setter

    def width(self, value):

        if not isinstance(value, int):

            raise ValueError('width must be an integer!')

        if value < 0 :

            raise ValueError('width must big than 0 !')

        self._width = value

    @property

    def height(self):

        return self._height   

    @height.setter

    def height(self, value):

        if not isinstance(value, int):

            raise ValueError('height must be an integer!')

        if value < 0 :

            raise ValueError('height must big than 0 !')

        self._height = value

    @property

    def resolution(self):

        return self._width*self._height