It's easier to calculate the map in this way, and add four points ABCD. * * * There are four situations:

The starting point is a, you can only go to point b, and there are two choices; There are two options from B to C (DB is a dead end); There are also two kinds of C to D; D to a are also two kinds; So 2*2*2*2= 16 kinds.

The starting point is C, which, like A, is 16;

3. The starting point is B, and the first one is C, which is also 2*2*2*2= 16; Go to D first, which is also 16 species; A ***32 species;

4. In the same way, the starting point is D, and there are 32 kinds like B;

So * * * is: 2*2*2*2*6=96.