import sys; input = sys.stdin.buffer.readline
sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

from math import pi

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	C = int(input())
	Rin, Rout = getlist()
	ans = C * pi ** 2 * (Rout + Rin) * ((Rout - Rin) ** 2) / 4
	print(ans)



if __name__ == '__main__':
	main()