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

using namespace std;

int main() {

	int q;
	double x;

	while(cin >> q) {
		if(q==-1)
			break;
		x=q/2;
		while(abs(x*x*x-q)>0.00001*q) {
			x=x-(x*x*x-q)/(3*x*x);
		}
		printf("%.6f\n", x);
	}

	return 0;

}