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