#include <cstdio>
#include <math.h>
using namespace std;

int q;
double x, x3, e;

int main(){
	while (scanf("%d", &q), q != -1) {
		e = 0.00001*q;
		x = q / 2.0;
		x3 = pow(x, 3);
		while (!(x3 - q < e && x3 - q > -e)) {
			x = x - (x3 - q) / (3 * pow(x, 2));
			x3 = pow(x, 3);
		}
		printf("%.6f\n", x);
	}


	return 0;
}