#include <cstdio>
#include <cmath>

int main(void){
	int q;

	while(scanf("%d", &q)){
		if(q == -1) break;
		double x = 0;
		x = q/2;
		while(x*x*x - q >= 0.00001*q){
			x = x - (x*x*x - q) / (3*x*x);
		}
		printf("%.6f\n", x);
	}


	return 0;
}