#include <iostream>
#include <cmath>
#include <cstdio>
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 nx = x-(x*x*x-q)/(3*x*x);
            x = nx;
        }
       cout<<x<<endl;
    }
    return 0;
}