#include<iostream>
#include<stdlib.h>
#include<stdio.h>

using namespace std;

int main(){

  int in;
  while(cin >> in){
    if(in == -1) break;
    double x = (double)in/2;
    while(1){
      if(labs(x*x*x - (double)in) < 0.00001+0.000001*(double)in){
	x = (2*x/3 + (double)in/(3*x*x));
	printf("%.6f\n",2*x/3 + (double)in/(3*x*x));
	break;
      }
      x = (2*x/3 + (double)in/(3*x*x));
    }
  }
  return 0;
}