# coding: utf-8
# yukicoder No.89 どんどんドーナツどーんといこう！

import math

cal = int(input())
r_in, r_out = map(int, input().split())

danmen = ((r_out - r_in) / 2) ** 2 * math.pi
circum = (r_in + r_out) * math.pi

vol_d = danmen * circum
total_cal = cal * vol_d

print("{:.6f}".format(total_cal))