let cal:Double = Double(readLine()!)!

let inpt = readLine()!.split(separator: " ").map{Int($0)!}

let r = Double(inpt[1]-inpt[0]) / 2.0

let r1 = Double(inpt[0]) + r
let r2 = r

let val:Double = 2.0 * r1 * r2 * r2 * Double.pi * Double.pi
let ans = val * cal
print(ans)