from math import *
import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]

def main():
    c=int(input())
    rin,rout=MI()
    r=(rout-rin)/2
    s=r*r*pi
    l=2*(rin+r)*pi
    v=s*l
    print(v*c)

main()