#include<iostream>
#include<algorithm>
#include<string>
#include<vector>
#include<bitset>
using namespace std;
double abs(double a){
    return (a<0)?-a:a;
}
int main(){
    int q;
    while(cin>>q,q!=-1){
        double x=(double)q/2;
        while(true){
            if(0.00001*q-abs(x*x*x-q)>0)break;
            x=x-(x*x*x-q)/(3*x*x);
        }
        cout<<fixed<<x<<endl;
    }
}