#include <iostream>
#include <iomanip>
#include <vector>
#include <cmath>
using namespace std;
double q;
double cal(double n){
  double ans;
  while(1){
    ans = n - n/3.0 - q/(3.0*n*n);
    //    cout << ans << endl;
    if(fabs(fabs(n*n*n)-fabs(q)) < 0.00001){
      return fabs(n);
    }
    n = ans;
    
  }
}

int main(){
  while(cin >> q,q != -1){
    cout  << fixed << setprecision(7) << cal(q/2.0) << endl;
  }
  return 0;
}