#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>
#include <stack>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <iostream>
#include <climits>
#include <cfloat>

using namespace std;

int main()
{
	while (true)
	{
		int q;
		scanf("%d", &q);
		if (q == -1)
			break;

		double x = q/2.0;
		while (abs(x*x*x - q) >= 0.00001*q)
			x = x - (x*x*x-q)/(3*x*x);
		printf("%.6f\n", x);
	}

	return 0;
}