#include <cmath>
#include <stdio.h>

double y(double x)
{
	return sqrt(4 - (x*x));
}

int main()
{
	double h = 0.5, x0 = 0.0, x1 = 0.5, x2 = 1.0;
	double Derivative = 0.0;
	Derivative = (1 / (h*h))*(y(x0)*(2 * x0 - x1 - x1) - 2 * y(x1)*(2 * x0 - x1 - x1) + y(x1)*(2 * x0 - x1 - x1));
	printf("%f\n", Derivative);


    return 0;
}