B'For a permutation p of numbers 1 through n , we define a stair array a as follows: a_i is length of the longest segment of permutation which contains position i and is made of consecutive values in sorted order: [x, x+1, ldots, y-1, y] or [y, y-1, ldots, x+1, x] for some x <= q y . For example, for permutation p = [4, 1, 2, 3, 7, 6, 5] we have a = [1, 3, 3, 3, 3, 3, 3] . You are given the stair array a . Your task is to calculate the number of permutations which have stair array equal to a . Since the number can be big, compute it modulo 998 ,244 ,353 . Note that this number can be equal to zero. The first line of input contains integer n ( 1 <= n <= 10^5 ) -- the length of a stair array a . The second line of input contains n integers a_1, a_2, ldots, a_n ( 1 <= a_i <= n ). Print the number of permutations which have stair array equal to a . Since the number can be big, compute it modulo 998 ,244 ,353 . '...