5.4. A coin is tossed repeatedly until three heads in a row appear. Let X,, record the current number of successive heads that have appeared. That is, X = 0 if the nth toss resulted in tails; X,, = 1 if the nth toss was heads and the (n - 1)st toss was tails; and so on. Model X,, as a success runs Markov chain by specifying the probabilities p, and q;.