# -*- coding: utf-8 -*-
"""
No.89 どんどんドーナツどーんといこう！
https://yukicoder.me/problems/no/89

"""
import sys
from sys import stdin
from math import pi
input = stdin.readline


def main(args):
    """
    https://ja.wikipedia.org/wiki/トーラス
    体積 V = 2 * pi**2 * r**2 * R
    外側の円の半径: R + r
    内側の円の半径: R - r
    """
    C = int(input())
    Rin, Rout = map(int, input().split())
    R = (Rin + Rout) / 2
    r = Rout - R
    V = 2 * pi**2 * r**2 * R
    ans = V * C
    print(ans)


if __name__ == '__main__':
    main(sys.argv[1:])