#include <iostream>
#include <stdio.h>
using namespace std;

int main() {
	long long int q;
	double ans;
	while(1){
		cin >> q;
		if(q==-1) break;
		double s = (double)q/2;
		while(1){
			ans = s - (s*s*s-q)/(3*s*s);
			if(ans < 0.00001*q) break;
			s = ans;
		}
		printf("%.6f\n",ans);
	}
	return 0;
}
