#include<iostream>
#include<cmath>
#include<iomanip>
using namespace std;

double Third_Root( double x , double q )
{
    if( fabs( x * x * x  - q ) < 0.00001 * q )
        return x;

    return Third_Root( x - ( x * x * x - q ) / ( 3 * x * x ), q );
}

int main()
{
    double x, q;

    while( cin >> q )
    {
        if( q == -1 )
            break;
        x = q / 2;
        cout << fixed << setprecision(6) << Third_Root( x, q ) << endl; 
    }
    return 0;
}
