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

int main() {
  int q;
  while(cin>>q, ~q) {
    double x = (double)q/2.;
    while(true) {
      if (abs(x*x*x - q) < 0.00001*q) break;
      x = x - (x*x*x-q)/(3*x*x);
    }
    printf("%.6f\n", x);
  }
}