#include <cstdio>
#include <cstdlib>
int main(){
	double r;
	while(scanf("%lf",&r) && r!=-1.0){
		double a=0.0;
		double b=r;
		while(1){
			double mid;
			mid=(a+b)/2;
			if(abs(mid*mid*mid-r)<0.00000001){
				printf("%f\n",mid);
				break;
			}else if(mid*mid*mid>r){
				b=mid;
			}else{
				a=mid;
			}
		}
	}
}