@staticmethod
def b():
    (n, *r) = map(int, sys.stdin.read().split())
    s = (np.pi * (np.array(([0] + r)) ** 2))
    s.sort()
    res = (s[n::(- 2)].sum() - s[(n - 1)::(- 2)].sum())
    print(res)
@staticmethod
def b():
    (n, *r) = map(int, sys.stdin.read().split())
    s = (np.pi * (np.array(([0] + r)) ** 2))
    s.sort()
    res = (s[n::(- 2)].sum() - s[(n - 1)::(- 2)].sum())
    print(res)