#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(1){   
                xx=x-((x*x*x-q)/(3*x*x));      
                
                if(fabs(x*x*x-q)<(0.00001*q)) break;
                x = xx;
            }          
            printf("%.7f\n",x);     
            }    
                
        return 0; 
}
