#include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;
int main(){
  double q;
  while(cin >> q && q != -1){
    double x = q / 2;
    while(true){
      if(fabs(x * x * x - q) < 0.00001 * q) break;
      x -= (x * x * x - q)/(x * x * 3);
    }
    cout << fixed << setprecision(7) << x << endl;
  }
}