#include <iostream>
#include <cmath>
using namespace std;
 
double f(double x)
{
        return 0.25 * (1.0 - 2.0 * x * x * x);
}
 
int main()
{
        double x = 0.11;
        double e = 0.00000005;
        while(abs(x - f(x)) > e)
        	x = f(x);
        cout << 2.0 * x * x * x + 4.0 * x - 1.0 << endl;
}