#include <bits/stdc++.h>
#define PB push_back
#define MP make_pair
#define REP(i,n) for (int i=0;i<(n);i++)
#define ALL(a) (a).begin(),(a).end()
#define INF 1000000001
#define MOD 10000
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> P;
const ull B=100000007;
double rec(double x,double q){
      return x-((x*x*x-q)/(3.0*x*x));
}
int main(){
      double q;
      while(cin>>q&&q!=-1){
            double x=(q/2.0,q);
            REP(i,1000){
                  x=rec(x,q);
            }
            printf("%.10f\n",x);
      }
}