#include <iostream>
#include <iomanip>
#include <algorithm>
using namespace std;

int main(){
	cout << fixed;
	cout << setprecision(10);
	while(1){
		int q;
		cin >> q;
		if(q == -1) break;
		
		double x = (double)q/2;
		while(abs(x*x*x -q) > 1e-5 *q){
			x = x - (x*x*x -q)/(3*x*x);
		}
		cout << x << endl;
	}
	return 0;
}
