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 a integer!')
    if value < 0:
        raise ValueError('width 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('height must be an integer!')
    if value < 0:
        raise ValueError('height must bigger than 0!')
    self._height = value

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