#include<iostream>
#include<cmath>
#include<iomanip>
using namespace std;
int x, cnt; double sum[10000];
int main() {
	while (true) {
		cin >> x; if (x == -1) { break; }
		sum[0] = x / 2.0; cnt = 0;
		while (abs(x - sum[cnt] * sum[cnt] * sum[cnt]) > 0.00001*x) {
			cnt++;
			sum[cnt] = sum[cnt - 1] - ((sum[cnt - 1] * sum[cnt - 1] * sum[cnt - 1] - x) / (3 * sum[cnt - 1] * sum[cnt - 1]));
		}
		cout << fixed << setprecision(20) << sum[cnt] << endl;
	}
}