#include <iostream>
#include <stdio.h>
using namespace std;
int main(){
	double x,q;
	while(cin>>q){
		if(q==-1) break;
		x = q/2;
		while(1){
			x=x-(x*x*x-q)/3/x/x;
			if(x*x*x-q < q*0.00001 && x*x*x-q > -q*0.00001) break;
		}
		printf("%.6lf\n",x);
	}
	return 0;
}