#include<iostream>
#include<stdio.h>
#include<cmath>
#define EPS 0.00000001
using namespace std;


bool eq(double x,double y){
  if(abs(x-y)<EPS)return true;
  else return false;
}

int n;
double q;
double t[1000000];
int main(){
  while(cin>>n){
    if(n==-1)break;
    t[1]=n/2.0;
    for(int i=1;i<1000000;i++){
      if(i==1)t[i]=n/2.0;
      else t[i]=t[i-1]-(t[i-1]*t[i-1]*t[i-1]-(double)n)/(3.0*t[i-1]*t[i-1]);

      if(eq(t[i]*t[i]*t[i],n)){
	//cout<<t[i]<<endl;
	printf("%.6f\n",t[i]);
	break;
      }
    }
    
  }
}