#include <iostream>
#include <cmath>

#define SQ(x) (x)*(x)
#define CU(x) (x)*(x)*(x)

using namespace std;

int main(void){
    int q;
    double x;
    double x_a;
    
    while(cin>>q,q!=-1){
        x=q/2.0;
        x_a=abs(CU(x)-q);
        while(x_a>=0.00001*q){
            x=x-(CU(x)-q)/(3*SQ(x));
            x_a=abs(CU(x)-q);
        }
        cout<<x<<endl;
    }
    return(0);
}