#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("%.6f\n",x);
            
    }
        
    return 0;
    
}
