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


bool isEnoughSmall(double q, double x) {
  return fabs(x*x*x-q) < 0.00001*q;
}

double solve(double q) {
  double x = q/2.0;
  while(!isEnoughSmall(q,x)) x = x - (x*x*x-q)/(3.0*x*x);
  return x;
}

int main() {
  double q;
  while(cin >> q && q != -1) printf("%.10f\n", solve(q));
  return 0;
}