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

int main() {
  int q;
  double x, xx, e;
  cout.setf(ios::fixed);
  while (cin >> q) {
    if (q == -1) break;
    x = q*0.5;
    while (1) {
      xx = x*x;
      e = xx*x - q;
      if (abs(e) < 1.0e-5 * q) break;
      x = x - e/(3.0*xx);
    }
    cout.precision(6);
    cout << x << endl;
  }
  return 0;
}