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

double thirdroot(double x,double q) {
  if(abs(x*x*x - q) < 0.00001 * q) {
    printf("%.6lf\n",x);
  }
  else if(abs(x*x*x - q) >= 0.00001 * q) {
    thirdroot(x - ((x*x*x - q) / (3 * x*x)),q);
  }
}

int main() {
  double q;
  while(cin >> q) {
    if(q == -1) break;
    thirdroot( q / 2.0,q);
  }
}