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

double deriv(double (*) (double),double,double);

main()
{
	double x=0.0,dx=0.001;
	printf("%f \n",deriv(cos,x,dx));
}

double deriv(double (*f) (double),double x,double dx)
{
	return ((f(x+dx) - f(x))/dx);
}