#include<cstdio>
#define eps 0.00001
double q;

double fabs(double a){
	if(a<0)return -a;
	return a;
}

int main(void){
	while(1){
		scanf("%lf",&q);
		if(q==-1)break;
		double x=q/2;
		while(fabs(x*x*x-q)>=eps*q){
			x=x-(x*x*x-q)/(3*x*x);
		}
		printf("%0.10f\n",x);
	}
	return 0;
}