#include <iostream>
#include <algorithm>
#include <cmath>
#include <iomanip>
using namespace std;
int main(void){
    long long q;
    double x[100], x1;
    while(cin >> q){
        if(q == -1) break;
        x[1] = q/2;
        for(int i = 2; ; i++){
            x[i] = x[i-1]-(x[i-1]*x[i-1]*x[i-1]-q)/(3*x[i-1]*x[i-1]);
            if(abs(x[i]*x[i]*x[i]-q) < 0.00001*q){
                x1 = x[i]; 
                break;
            }
        }
        cout <<fixed;
        cout << setprecision(7) << x1 << endl;
    } 
    return 0;
}

