#include <iostream>
#include <cmath>
#include <cstdio>
using namespace std;

int q;

bool input() {
	cin >> q;
	if(q == -1)
		return false;
	return true;
}

double solve() {
	double x = (double)q / 2;
	while(fabs(x * x * x - q) >= 0.00001 * q) {
		x = x - x / 3 + q / (3 * x * x);
	}

	return x;
}

int main(void) {
	while(input())
		printf("%.8f\n", solve());
}