#include <cmath>
#include <cstdio>
using namespace std;

int main(){
	double x, q, y;
	while(scanf("%lf", &q), q >= 0.0){
		x = 0.5 * q;
		while(1){
			y = x * x * x - q;
			if(abs(y) < 1e-5 * q){
				break;
			}
			x -= y / (3.0 * x * x);
		}
		printf("%.15f\n", x);
	}
}