def main():
    import math

    math.pi

    c = float(input())
    r_in, r_out = [int(i) for i in input().split(" ")]
    r = (r_out - r_in) / 2

    v = 2 * (math.pi**2) * (r**2) * (r_in + r)

    ans = c * v
    print(ans)


if __name__ == "__main__":
    main()