#include <iostream>
#include <iomanip>
#include <algorithm>
using namespace std;

double t_root(double q){
	double x = q / 2;
	while(max(x * x * x  - q,-(x * x * x - q)) >= 0.000001 * q){
		x = x - (x * x * x - q) / (3 * x * x);
	}
	return x;
}

int main(){
	double q;
	while(cin >> q){
		if(q == -1) break;
		cout << fixed << setprecision(6) <<  t_root(q) << endl;
	}
	return 0;
}