//58
#include<iostream>
#include<cmath>
#include<iomanip>

using namespace std;

int main(){
  for(double q;cin>>q,q!=-1;){
    double x=q/2;
    while(q!=0&&!(fabs(x*x*x-q)<0.00001*q)){
      x=x-(x*x*x-q)/3/x/x;
    }
    cout<<fixed<<setprecision(6)<<x<<endl;
  }
  return 0;
}