#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for (int i = x; i < n; i++)
#define OP(m) cout << m << endl
typedef long long ll;
typedef unsigned long long ull;

int main()
{
    double q, x;
    while (cin >> q, q != -1)
    {
        x = q / 2;
        while (abs(x * x * x - q) >= 0.00001 * q)
            x = x - (x * x * x - q) / (3 * x * x);
        printf("%.8f\n", x);
    }
    return 0;
}
