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

int main(){
	int n;
	double q,a,b,c;
	while(cin >> n, n != -1){
		q = (double)(n) / 2.0;
		while(abs(q * q * q - (double)(n)) > (0.00001 * n)){
		/*	a = q * q * q;
			b = q * q;
			c = (a - q)/(3 * b);*/
			q = q - (q * q * q - (double)(n))/(3 * q * q);
		}
		cout << fixed << setprecision(6) << q << endl;
	}
}