#include <bits/stdc++.h>
//typedef unsigned long long int ull;
using namespace std;

double temp(double,double);

double temp(double x,double q){
    x-=(x*x*x-q)/(3*x*x);
    return x;
}

int main(){
    double x,q;
    while(1){
        cin>>q;
        if(q==-1)break;
        x=q/2;
        do{
            x=temp(x,q);
        }while(abs(x*x*x-q)>=1e-5*q);
        cout<<x<<endl;
    }
}