#include <iostream>
using namespace std;
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
long double lfabs(long double a)
{
   if(a < 0) a *= -1;
   return a;
}

int main()
{
   int i,j,k,l;
   long double x;
   int q;
   while(1) {
      cin >> q;
      if(q == -1) break;

      x = (long double)q/2;
      while(1) {
         x = x - (x*x*x - q) / (3*x*x) ;
         if( lfabs(x*x*x-q) < 0.00001*q ) break;
      }
      printf("%llf\n",x);
   }
   
   return 0;
}