Fibonacci 数列递归 重复计算

public class Fibonacci{
public static long F(long n){
System.out.println("call F" + n);
if (n == 0) return 0;
if (n == 1) return 1;
long t = F(n-1) + F (n-2);
System.out.println("return " + t);
return t;
}
public static void main(String[] args)
{
long N = Long.parseLong(args[0]);
System.out.println(N+"th Fibonacci number is " + F(N));
}
}

java Fibonacci 4
call F4
call F3
call F2
call F1
call F0
return 1
call F1
return 2
call F2
call F1
call F0
return 1
return 3
4th Fibonacci number is 3