#include <iostream>
#include <vector>
#include <list>
#include <algorithm>
#include <string>
#include <sstream>
#include <stack>
#include <iomanip>
#include <numeric>
#include <queue>
#include <climits>
#include <set>
#include <complex>
#include <cmath>
#include <cstring>
#include <map>
using namespace std;
using ll = long long;
#define MOD 1000000007
#define INF 1LL << 59

double x[1010], y[1010];
int main()
{
    //std::ios::sync_with_stdio(false);
    //std::cin.tie(0);
    cout << fixed << setprecision(7);

    long double n;
    while (cin >> n)
    {
        if (n == -1)
            break;
        long double x[101000];
        long double t = n;
        x[1] = t / 2.0;
        int idx = 2;
        while (1)
        {
            x[idx] = x[idx - 1] - (x[idx - 1] * x[idx - 1] * x[idx - 1] - n) / (3 * (x[idx - 1] * x[idx - 1]));

            if (abs(x[idx] * x[idx] * x[idx] - n) < 0.00001 * n)
                break;
            idx++;
        }
        cout << x[idx] << endl;
    }
    return 0;
}
