#include<iostream>
#include<cmath>

using namespace std;

int main(){
  double q,x;
  while(cin>>q){
    if (q==-1)break;
    x = q/2;
    while(abs(x*x*x-q)>=0.00001*q){
      x = x-(x*x*x-q)/(3*x*x);
    }
    cout<<x<<endl;
  }
}