import sys
import math


def input(): return sys.stdin.readline().rstrip()


def main():
    C = int(input())
    Rin, Rout = map(int, input().split())
    print(C * math.pi**2 / 4 * (Rin+Rout) * (Rout-Rin)**2)


if __name__ == '__main__':
    main()