#include <math.h>
#include <stdio.h>


using namespace std;

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

int main()
{
    double x = 1.0, h = 0.01;
    double fc;
    //fc = (f(x+h) - f(x-h))/(2*h);
    //fc = (f(x) - f(x - h)) / h;
    fc = (f(x + h) - f(x)) / h;
	printf("%f\n", fc);

    return 0;
}