#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 n) {
	double x = q/2.0;
	for (int i = 0;i != n;++i) {
		x = x - (x*x*x - q)/(3*x*x);
	}
	return x;
}

int main() {
	int q;
	while (cin >> q && ~q) {
		cout << setiosflags(ios_base::fixed) << setprecision(6) << third_root((double)q,100000) << endl;
	}
}