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

using namespace std;

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