#include <iostream>
#include <cstdio>
#include <cmath>
#define EQ(a,b) (abs(a - b) < 0.000000001)
using namespace std;

const double INF = (1 << 31) - 1;

int main ()
{
    double q;
    while (cin >> q, q >= 0) {
        double ub = INF, lb = -1;
        while (!EQ(ub,lb)) {
            double mid  = (ub + lb) / 2.0;
            if (mid * mid * mid > q) {
                ub = mid;
            } else {
                lb = mid;
            }
        }
        printf("%.6f\n", lb);
    }

    return 0;
}