Common Knowledge:

A particular fact F is said to be 'common knowledge' between the players if each player knows F, each player knows that the other know F, each player knows that every other player knows that each player knows F, and so on.

Let's play a game:

Imagine a game where without showing your neighbour your strategy, put yourself in other peoples' shoes, and enter in a whole number between 1 and 100. We will calculate the average number, and the winner is the one who guesses the number two-thirds times the average number. The winner will earn 3000 SATs.

What would be the perfect answer?