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