#include <iostream>
#include <cmath>
#include <iomanip>

using namespace std;

long double thrt(long double q){
  long double x=q/2.0;
  while(abs(x*x*x-q)>=0.00001*q){
    x-=(x*x*x-q)/(3.0*x*x);
  }
  return x;
}

int main(){
  long double q;
  while(cin>>q&&(q!=-1)){
    cout<<setprecision(7)<<thrt(q)<<endl;
  }

}