#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

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