#include <cstdio>
#include <iostream>

using std::cin;
using std::printf;

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) {
		printf("%lf\n",third_root((double)q,100000));
	}
}