#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("%.7f\n",zenka(q));     
                }  
                }     
    return 0;
        
    }

