class Point(tuple):
    def __new__(cls, x, y):
        return tuple.__new__(cls, (y, x))
    def __getattr__(self, name):
        if name == "x":
            return self[1]
        elif name == 'y':
            return self[0]
        else:
            raise AttributeError
    def __repr__(self):
        return '<Point(%d, %d)>' % (self[1], self[0])

    def xy(self):
        return (self[1], self[0])
    def add(self, x, y):
        assert x >= 0, y >= 0
        return Point(self[1] + x, self[0] + y)
    def vadd(self, x, y):
        assert x >= 0, y >= 0
        if y > 0:
            return Point(x, self[0] + y)
        else:
            return Point(self[1] + x, self[0])