#include <iostream>
#include <cmath>
#include <cfloat>
#include <iomanip>
using namespace std;
double f(double x, double q){
    return pow(x, 3.0) - q;
}

double df(double x){
    return 3.0 * pow(x, 2.0);
}

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 q, x;
    while(cin >> q){
        if(q == -1) break;
        x = q / 2.0;
        cout << fixed << setprecision(6) << newton(x, q) << endl;
    }
    return 0;
}

