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

double x, q, n;

int hantei(double x, double q){
	double z = 0.00001 * q;
	double zz = pow(x, 3) - q;
	if (z > fabs(zz)) { return 0; }
	else { return 1; }
}

double zen(double x, double q){
	double ans = x - (pow(x, 3) - q) / 3 / pow(x, 2);
	return ans;
}

int main(){
	while(cin >> q){
		if (q == -1) { break; }
		x = zen(q / 2, q);
		n = hantei(x, q);
		while(n != 0){
			x = zen(x, q);
			n = hantei(x, q);
		}
		cout << x << endl;
	}
	return 0;
}