#include "bits/stdc++.h"
using namespace std;
typedef long long ll;

int main(){

    for(double q;cin>>q;){
        if(q<0)break;
        double x = q / 2;
        while(1){
            if(abs(x*x*x-q) < 0.00001 * q)break;
            double xx = x - (x * x * x - q) / (3 * x * x);
            x = xx;
        }
        printf("%.10f\n", x);
    }

    return 0;
}
