#include<iostream>
#include<stdio.h>
#define EPS 0.00000001
using namespace std;
typedef long long ll;

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

ll n;
double q;
double t[10000];
int main(){
  while(cin>>n){
    if(n==-1)break;
    t[1]=n/2.0;
    for(int i=2;i<10000;i++){
      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;
      }
    }
    
  }
}