 #include<iostream>
 #include<stdio.h>
 #include<string>
 #include<math.h>
 #include<iomanip>
 #include<algorithm>
 #include<string.h>
 #include<cctype>
 #include<map>
 #include<set>
 #include<vector>
 #include<sstream>
 #include<stack>
 #include<queue>
 #include<deque>
 #include<functional>
 #include<utility>
 
 using namespace std;
 
 double abs(double x)
 {
   if(x>=0) return x;
   else return -x;       
 }
 
 int main()
 {
   long long int q;
   while(cin>>q&&(q!=-1))
   {
     double x;
     x=(1.0*q)/2;
     while(abs(pow(x,3)-q)>=(0.00001*q))
     {
       x=1.0*2/3*x+q/(3*x*x);                                
     }                        
     printf("%.6lf\n",x);
   }
   //while(1);
   return 0; 
 }