import math

def main():
    C = int(input())
    R_IN, R_OUT = map(int, input().split())
    pi = math.pi

    r = (R_OUT - R_IN) / 2
    g = ((R_OUT - R_IN) / 2) + R_IN
    volume = 2 * (pi ** 2) *  (r ** 2) * g
    print(C * volume)

if __name__ == '__main__':
    main()