#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
typedef long long ll;

double eps, alterX;
ll q;

//漸化式
double formula() {
    return(alterX - ((alterX*alterX*alterX - q) / (3 * (alterX*alterX))));
}
//ループ
void solve() {
    while(alterX*alterX*alterX - q > eps) { //|x^3 - q| <= epsの時終了
        alterX = formula();
    }
}
//出力
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);
    }
}