n = int(input()) a = list(map(int, input().split())) max_val = 1 for i in range(0, n - 1): if a[i] - a[i - 1] <= 2: max_val = 2 for i in range(1, n - 1): if a[i + 1] + a[i - 1] == 2 * a[i]: max_val = 3 print(max_val)