#include <iostream>
#include <cstdio>
#include <stack>
#include <iomanip>
using namespace std;

double abs(double x) {
    if (x < 0) return -x;
    return x;
}

#define EPS 1e-10
double solve(double x, double q) {
    stack<double> st;
    st.push(x);
    int count = 0;
    while (!st.empty()) {
        double _x = st.top(); st.pop();
//        cout << _x << endl;
        if (abs(_x * _x * _x - q) < q * EPS) return _x;
        st.push(_x - (_x * _x * _x - q) / (3 * _x * _x));
    }
}

int main() {
    int q;
    while (cin >> q) {
        if (q == -1) break;
        printf("%.6lf\n", solve(q / 2.0, q));
    }
    return 0;
}
   