#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("%.7f\n",zenka(q));
       }
   }
     return 0;
}
