#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
int main(void)
{
    int a;
    while(cin>>a)
     {
        if(a==-1)break;
        double q = (double)a;
        double x = q/2;
        while(abs(x*x*x-q)>=0.00001*q)
         {    
            double y = x-(x*x*x-q)/(3*x*x);
            x = y;
        }
        cout<<set.precision(6)<<fixed;
        cout<<x<endl;
    }
    return 0;
}