There are n children around a round table. Erika is the oldest among them and she has n candies, while no other child has any candy. Erika decided to distribute the candies according to the following rules. In every round, she chooses a child with at least two candies and the chosen child sends a candy to each of his/her two neighbors. (So in the first round Erika must choose herself). For which n≥3 is it possible to end the distribution after a finite number of rounds with every child having exactly one candy? invariantmodular arithmeticarithmetic sequencealgebrasystem of equationsIMO Shortlistcombinatorics unsolved