#include <bits/stdc++.h>
using namespace std;
int q;

bool isEnoughSmall(double x) {
    return(abs(x*x*x - q) < 0.00001*q);
}

double formula(double beforeX) {
    return(beforeX - ((beforeX*beforeX*beforeX-q) / (double)(3.0*beforeX*beforeX)));
}

void solve() {
    double nowx = q / 2.0;
    while(true) {
        nowx = formula(nowx);
        if(isEnoughSmall(nowx)) break;
        //printf("exec:%.6f\n", nowx);
    }
    printf("%.6f\n", nowx);
}

int main(void) {
    while(cin >> q, q != -1) {
        solve();
    }
    return(0);
}