#include <iostream>
#include <iomanip>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>

using namespace std;

int main() {
	double q;
	while (cin >> q && q != -1) {
		double x = q / 2;
		while (1) {
			double n = pow(x, 3) - q;
			if (fabs(n) < 0.00001)
				break;
			x = x - (n / (3 * pow(x, 2)));
		}
		cout << fixed << setprecision(6) << x << endl;
	}
	return 0;
}