#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>

using namespace std;

int main(){
	
	double q, x;
	
	while(true){
		
		scanf("%lf", &q);
		
		if(q < 0){
			break;
		}
		
		x = q / 2;
		
		while(true){
			if(x * x * x - q < q * 0.00001){
				break;
			}
			x -= (x * x * x - q) / (3 * x * x);
		}
		
		printf("%.10f\n", x);
		
	}
	return 0;
}