#include <stdio.h>
#include <math.h>
int main(void){
	int q;
	while(scanf("%d", &q))
	{      
		if(q==-1) break;
		double x;
		x=q/2;
		while(fabs(x*x*x-q)>0.00001*(double)q){
			x=x-(x*x*x-q)/(3*x*x);
		}
		printf("%.6f\n",x);
	}
}

