#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
double eps, alterX;
int q;

double formula() {
    return(alterX - ((alterX*alterX*alterX - q) / (3 * (alterX*alterX))));
}

void solve() {
    while(alterX*alterX*alterX - q > eps) {
        alterX = formula();
    }
    
}

void output(double ans) {
    printf("%.6f\n", ans);
}

int main(void) {
    while(cin >> q, q != -1) {
        alterX = q / 2.0; //X1
        eps = q / 100000.0; //EPS
        solve();
        output(alterX);
    }
}