Please answer the following question with steps, thank you

Let X1 -> X2 -> X3 ... > Xn forms a Markov chain in this order. Thus, the joint probability of X1, . . .. Xn are given by p(x1, x - 2, . .., Xn) = p(xaxn-1)p(Xn-1/xn-2) . . . p(x2/x1 )p(x1). Reduce I(X1; X2, ..., X ) to its simplest form (show your work). [6 Marks]