#include <iostream>
#include <cstdio>
#include <cmath>

using namespace std;

bool C(long double x, long double q) {
	return x*x*x < q;
}

int main() {
	long double q;
	while (cin >> q) {
		if (q == -1.0) {
			break;
		} else if(q == 1.0) {
			cout << 1.0 << endl;
		} else {
			long double lb = 0;
			long double ub = q/2.0;
			for (int i = 0; i < 100; i++) {
				long double mid = (lb+ub) / 2.0;
				if (C(mid, q)) lb = mid;
				else ub = mid;
			}
			printf("%.6Lf\n", ub);
		}
	}
	return 0;
}