#include <stdio.h>
#define EPS 0.00001

int main(void) {
	int n,i;
	double x[1000];
	double x2;
	double x3;
	while (scanf("%d", &n), n!=-1) {
		x[0] = (double)n / 2;
		i = 0;
		x3 = x[i] * x[i] * x[i];
		while (!(-EPS*(double)n < x3-(double)n && x3-(double)n < EPS*(double)n)){
			x2 = x[i] * x[i];
			x3 = x[i] * x[i] * x[i];
			x[i + 1] = x[i] - ((x3 - n) / (3 * x2));
			i++;
		}
		printf("%f\n", x[i]);
	}
	return 0;
}