from math import pi


def main():
    C = int(input())
    Ri, Ro = map(int, input().split())

    circle_cut_area = pi * (Ro-Ri)**2 / 4

    length = 2 * pi * (Ri + (Ro-Ri)/2)

    print(C*length*circle_cut_area)


if __name__ == "__main__":
    main()