#include <cstdio>
#include <cstdlib>
double abs(double t){
	if(t<0.0){
		return -1.0*t;
	}else{
		return t;
	}
}
int main(){
	double r;
	while(scanf("%lf",&r) && r!=-1.0){
		double e=r/2.0;
		for(;;){
			e=(e-(e*e*e-r)/(3*e*e));
			if(abs((double)e*e*e-(double)r)<0.00001*r){
				printf("%f\n",e);
				break;
			}
		}
	}
}