#include <iostream>
#include <cmath>

using namespace std;

long double thirdroot(long double q);

int main(){
  long double q=0;
  for(;;){
    cin>>q;
    if( q==-1 ) break;
    cout<<thirdroot(q)<<endl;
  }
  return 0;
}

long double thirdroot(long double q){
  long double x=q/2;
  while( abs(x*x*x-q)>=0.00001*q ){
    x-=(x*x*x-q)/(3.0*x*x);
  }
  return x;
}