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