#include <stdio.h>
#define EPS 0.00001

int main(void) {
	int n,i;
	double x;
	double x2;
	double x3;
	while (scanf("%d", &n), n!=-1) {
		x = (double)n / 2;
		i = 0;
		x3 = x * x * x;
		while (!(-EPS*(double)n < x3-(double)n && x3-(double)n < EPS*(double)n)){
			x2 = x * x;
			x3 = x * x * x;
			x = x - ((x3 - n) / (3 * x2));
			i++;
		}
		printf("%f\n", x);
	}
	return 0;
}