import scala.io.StdIn.readDouble

object Main extends App {
  def cubeRoot(q:Double) = {
    def f(x:Double):Double = {
      val x3 = x*x*x
      if( Math.abs(x3-q) < 0.00001*q ) x
      else f(x- (x3-q)/(3*x*x))
    }
    f(q/2)
  }
  var x = 0D
  while( {x=readDouble;x} != -1D ) {
    println(cubeRoot(x))
  }
}