The output is 16, I m confused. Could you please explain how the function works?

public class 02 ( public static void main(String[] args) f // TODO Auto-generated method stub System.out.println(f (20)); 9e static long f(long n) f if (n--0) return 0; else if(n==1) return 1; else 1 12 13 14 15 16 17 18 19 return f(n/2)+f(n/2); 20