#include <iostream>
#include <cmath>
#include <cstdio>
const double eps = 0.00001;
using namespace std;

int main(void) {
    int q;
    while (1) {
        cin >> q;
        if (q == -1) break;

        double bx = q/2.0;
        do {
            double ax = bx - (bx*bx*bx - q)/(3*bx*bx);
            bx = ax;
        } while (abs(bx*bx*bx-q) >= eps*q);
        printf("%.7f\n", bx);
    }

    return 0;
}