#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using pii = pair<int, int>;

int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(false);
  cout << fixed << setprecision(10);
  
  int q;
  while (cin >> q, q != -1) {
    double x = q / 2.;
    while (!(abs(x * x * x - q) - 0.00001 * q < -1e-10)) {
      x = x - (x * x * x - q) / (3. * x * x);
    }
    cout << x << endl;
  }

  return 0;
}
