AMO 2020 Problem 2

Amy and Bee play the following game. Initially, there are three piles, each containing 2020 stones. The players take turns to make a move, with Amy going first. Each move consists of choosing one of the piles available, removing the unchosen pile(s) from the game, and then dividing the chosen pile into 2 or 3 non-empty piles. A player looses the game if they are unable to make a move.

Prove that Bee can always win the game,no matter how Amy plays