#include <bits/stdc++.h>

using namespace std;

typedef long long int ll;

double ret(ll q) {
	double x = q / 2., th = 0.00001 * q;
	do {
		double next = x / 3 * 2 + q / (3 * x * x);
		x = next;
	} while(abs(pow(x, 3) - q) > th);
	return x;
}

int main() {
	ll x;
	while(cin >> x, x != -1) {
		cout << fixed << setprecision(6) << ret(x) << endl;
	}
	return 0;
}

