func main()
	var C: float :: cui@input().toFloat(&)
	var _: [][]char :: cui@input().split(" ")
	var r1: float :: _[0].toFloat(&)
	var r2: float :: _[1].toFloat(&)
	var rr: float :: (r2 - r1) / 2.0
	var ans: float :: C * 2.0 * lib@pi ^ 2.0 * (r1 + rr) * rr ^ 2.0
	do cui@print("\{ans.toStrFmt(".10f")}\n")
end func