class Screen(object):
    @property
    def width(self):
        return self._width
    @width.setter
    def width(self,value):
        if not isinstance(value, int):
            raise ValueError('input must be an integer!')
        if value < 0:
            raise ValueError('input must bigger 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('input must be an integer!')
        if value < 0:
            raise ValueError('input must bigger than 0!')
        self._height=value

    @property
    def resolution(self):
        return self._width*self._height