#include <iostream>
#include <cmath>
#include <cstdio>
using namespace std;
#define EPS 1e-5
int main(void){
  double q,x;
  int times;


  while(cin >> q){
	if(q == -1) break;
	x = q / 2;
	
	while(fabs(pow(x,3) - q) >= EPS * q){
	  x = x - (pow(x, 3) - q) / (3 * pow(x,2)); 
	}
	printf("%.6f\n", x);
  }
}