Six positions, numbered 0 to 5, are arranged on a circle. A particle moves around the circle as follows. With probability 1/3 the particle moves counter-clockwise two positions, with probability 1/3 the particle moves clockwise one position, and with probability 1/3 the particle stays where it is. Let Xn denote the location of the particle after n moves. How many communications classes does the Markov chain Xn have?