#include <iostream>
#include <cstdio>
#include <cmath>
#include <iomanip>

using namespace std;

double f(double x, double q) {
   
    return (x * x * x - q);
}

double df(double x) {
    return (3 * x * x);
}

double newton(double x, double q) {
    
    if(abs(f(x, q)) < 0.00001 * q) {
        return x; 
  }
    return newton(x - f(x, q)/df(x),q);
}

int main(void){
    double x;
    double q;
    while(cin >> q){
        if(q == -1) break;
        x = q/2;
        cout << fixed << setprecision(6) << newton(x,q) << endl;
    }
}

