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

using namespace std;

double make(double in){
  int i = (double)in;
  int k = 0;
  while(i){
    k++;
    i/=10;
  }
  for(int i = 0; i < 5+k; i++) in/=10;
  return 0.0001+in;

}

int main(){

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