```
int f(int n){
  if (n==0 || n==1)
    return 1;
  else 
    return 2*f(n-1)+2*f(n-2);
}

```

How do you think this in steps, if n=3?
If there was only one "2\*f(n-1)", I would have known how to think it, but there are two calls.
Thanks!