#include<stdio.h>
#include <algorithm>
#include <cassert>
#include <cctype>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <iostream>
#include <iterator>
#include <list>
#include <map>     
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <iomanip>
#include <stack>
#include <string>
#include <vector>
using namespace std;
#define ll long long
#define ld long double
#define rep(a,t) for(int a=0;a<t;a++) 
#define forever while(true)
#define Sort(a) sort(a.begin(),a.end())
#define Reverse(a) reverse(a.begin(),a.end())
#define pb push_back
int main()
{
	cin.tie(0);
	ios::sync_with_stdio(false);
	ld a = 0;
	while (true) {
		cin >> a;
		if (a == -1) { break; }
		ld x = a / (ld)2;
		while (abs(x * x * x - a) >= 0.00001*a) {
			x = x - (x * x * x - a) / (3 * x * x);
		}
		cout << x << endl;
	}

	return 0;
}
