#include<iostream>
#include<cmath>
#include<vector>
#include<string>
#include<cstdio>
typedef unsigned long long ull;
#define rep(i,a) for(int i=0;i<a;i++)
#define loop(i,a,b) for(int i=a;i<b;i++)
using namespace std;
const double eps = 0.00001;
const double pi = acos(-1);
const double inf = (int)1e5;

int main(void){
  double N;
  while(cin>>N,N!=-1){
    double q =1.0*N/2;
    int i = 0;
    while(abs(pow(q,3)-N)>eps*N&&i<10000){
      i++;
      //printf("%.10f\n",q);
      q=q-(pow(q,3)-N)/(3*pow(q,2));
    }
    printf("%.6f\n",q);
  }
}