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

bool finish(double q, double x) {
  return abs(x*x*x - q) < 0.00001 * q;
}

int main() {
  double q, x;
  while(cin >> q && q != -1) {
    x = q/2.0;
    while(!finish(q, x)) {
      x = x - (x*x*x - q)/(3*x*x);
    }
    printf("%.6f\n", x);
  }
  return 0;
}