class Smartphone:
    def __init__(self):
        self.battery_level = 100

    def use(self, amount):
        self.battery_level -= amount
        if self.battery_level < 0:
            self.battery_level = 0

    def charge(self, amount):
        self.battery_level += amount
        if self.battery_level > 100:
            self.battery_level = 100

phone = Smartphone()
phone.use(30)
print(phone.battery_level)  

phone.charge(30)
print(phone.battery_level)