can you help me with this question? thanks

4. Twenty penguins are standing in a circle. All at once, each penguin randomly decides to slap one of its two neighbours with its ipper! What is the expected number of penguins who are not slapped by either of their neighbours? (You can assume that each penguin slaps the penguin to its left With probability 1/2 and the penguin to its right With probability 1/2.)