#include <iomanip>
#include <iostream>

using std::cin;
using std::cout;
using std::endl;
using std::ios_base;
using std::setiosflags;
using std::setprecision;

double third_root(double q,int i) {
	if (i == 1) {
		return q/2;
	}
	double x = third_root(q,i-1);
	return x - (x*x*x - q)/(3*x*x);
}

int main() {
	int q;
	while (cin >> q && ~q) {
		cout << setiosflags(ios_base::fixed) << setprecision(6) << third_root((double)q,10) << endl;
	}
}