class Screen(object):
    @property
    def width(self):
      return self._width
    @width.setter
    def width(self,value):
      self._width=value
    @property
    def height(self):
      return self._height
    @height.setter
    def height(self,value):
      self._height=value
    @property
    def resolution(self):
      return self._width*self._height
