# No.89 どんどんドーナツどーんといこう！
import math

c = int(input())
r_in, r_out = [int(i) for i in input().split()]

print('{:.10f}'.format(math.pi ** 2 * (r_in + r_out) * (r_out - r_in) ** 2 / 4 * c))