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

using namespace std;

int main() {
	long long int n;
	while (cin >> n) {
		if (n == -1) {
			break;
		}
		long double q;
		q = (long double)n / 2.0;
		while (q > (2 << 9) || fabs(q*q*q-n) >= 0.00001*q) {
			q = (2.0 * q / 3.0) + ((n/3.0)/q)/q;
		}
		printf("%.6f\n", q);
	}
	return 0;
}