import math

C = int(input())
R_in, R_out = map(int, input().split())

r = (R_out - R_in) / 2.0
R = (R_in + R_out) / 2.0

volume = 2 * (math.pi ** 2) * (r ** 2) * R
kcal = C * volume

print("{0:.10f}".format(kcal))