#include <stdio.h>
double zenka(double q)
{    
    double x=q/2;
    while(x*x*x-q>=0.00001*q || x*x*x-q<=-0.00001*q)
    {        
        x=x-((x*x*x)-q)/(3*x*x);    
        
    }        
    return x;
    
}
int main(void)
{    
    int q;        
    while(1)    
    {        
        scanf("%d",&q);        
        if(q==-1) break;        
        else        
        {            
            printf("%.6f\n",zenka(q));        
            
        }    
        
    }        return 0;}
