#include <bits/stdc++.h>
using namespace std;

int main(){
    double x,y,q;
    while(cin>>x,q>=0.0){
        x=q/2;
        while(1){
            y=x*x*x-q;
            if(abs(y)<1e-5*q)break;
            x-=y/(3*x*x);
        }
        cout<<x<<endl;
    }
}