#include <stdio.h>
#include <math.h>
int main(void){
    double q; 
    while(scanf("%lf", &q)!= EOF && q != -1) { 
        double x, a;       
        x=q/2;       
            while(1){
                if(fabs(x*x*x-q)<0.00001*q) break;
                x=x-((x*x*x-q)/(3*x*x));
                x = x;
            }          
            printf("%.7f\n",x);     
            }    
                
        return 0; 
}
