# -*- coding:utf-8 -*-
#案例：计算正方形的面积和周长
x = 8
class Circle:
    def __init__(self,n):
        self.n = n
    def area(self):
        return self.n*self.n
    def perimeter(self):
        return self.n*4
class Ring:
    def __init__(self,out_n,int_n):
        self.out_c = Circle(out_n)
        self.int_c = Circle(int_n)
    def area(self):
        return self.out_c.area() - self.int_c.area()
    def perimeter(self):
        return self.out_c.perimeter() + self.int_c.perimeter()

ring = Ring(20,10)
print(ring.area())
print(ring.perimeter())