I think of a number in the range 1 to 4. You try to guess what it is.

Assuming your guess was incorrect I must now change my number to either one more or one less than my previous number (but still within the range 1 to 4). You try to guess again.

We continue like this, with me changing to an adjacent number and you guessing what my current number might be.

What strategy could you come up with that will always successfully guess my number within 4 guesses?