#include <iostream>
#include <stdio.h>
#include <math.h>
#include <iomanip>

using namespace std;

double third_root(double xn, double q){
    if((xn*xn*xn-q)>-0.00001*q  &&  (xn*xn*xn-q)<0.00001*q){
        return xn;
    }
    
    xn = xn-((xn*xn*xn-q))/(3.0*xn*xn);
    return third_root(xn, q);
    
}


int main(void)
{
    long long int q;
    while(cin>>q){
        if(q==-1)break;
        printf("%.6f\n",third_root((double)q/2.0, (double)q));
    }
}