#include <iostream>
#include <sstream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <queue>
#include <cmath>
#include <set>
#include <map>
#include <cstdlib>
#include <cstdio>
using namespace std;

const double EPS = 1e-9;

double tr(double xn, double q){
	double xn2 = xn*xn;
	double xn3 = xn2*xn;
	if(abs(xn3 - q) < 0.00001*q){
		return xn;
	}
	return tr(xn-(xn3-q)/(3.0*xn2), q);
}

int main(){
	int q;
	while(cin >> q, q != -1){
		printf("%lf\n", tr(q/2.0, q));
	}

	return 0;
}