#include <iostream>
#include <cmath>
#include <cstdio>
#define EPS 1e-5
using namespace std;

int main(){
    double q;
    while(true){
        cin >> q; if(q == -1) break;
        double x = q/2;
        while(true){
            if(fabs(x*x*x-q) < EPS*q) break;
            x -= (x*x*x-q)/(x*x*3);
        }
        printf("%f\n",x);
    }
}