#include <cstdio>
#include <stack>
#include <cmath>
using namespace std;
int main()
{
	int q;
	stack<double> x;
	while (scanf("%d", &q))
	{
		if (q == -1) break;
		x.push((double)q/2);
		while (abs(x.top()*x.top()*x.top() - q) >= 0.00001*(double)q)
			x.push(x.top() - (x.top()*x.top()*x.top() - q)/(3*x.top()*x.top()));
		printf("%.6f\n", x.top());
	}
}