class shop:
    def __init__(self):
           print("welcome!")
class sell(shop):
    def __init__(self):
        super().__init__(name)
        self.P = 0
    def use(sc,self):
        self.P += sc
class buy(shop):
    def __init__(self):
        super().__init__(name)
        self.P = []
    def use(sc,self):
        self.P.append(sc)
print('Hello world!')