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

using namespace std;

int main()
{
    int q; double x;
    
    while(true)
    {
        cin >> q;
        
        if(q == -1) { break; }
        
        x = q / 2.0;
        
        while(abs(x * x * x - q) >= 0.00001 * q)
        {
            x = x - (x * x * x - q) / (3 * x * x);
        }
        
        cout << fixed << setprecision(12) << x << endl;
    }
    
    return 0;
}