#include <iostream>
#include <cmath>

using namespace std;

int main() {
  while (true) {
    double q;
    cin >> q;
    if (q == -1.)
      break;

    double x = q / 2;
    while (0.00001 * q <= abs(pow(x, 3) - q))
      x -= (pow(x, 3) - q) / (3 * x * x);

    printf("%.10lf\n", x);
  }
}
