#include<iostream>
#include<cstdio>
using namespace std;
int main(){
  double q;
  while(cin >>q,q!=-1){
    double ans = q/2;
    for(;;){
      ans = ans-((ans*ans*ans)-q)/(3*ans*ans);
      if(ans*ans*ans-q<q*0.00001 && -q*0.00001<ans*ans*ans-q) break;
    }
    printf("%.6lf\n",ans);
  }
  return 0;
}