def check_is_pine_decoration(lst:list):
    if len(set(lst)) != 3:
        return False
    second = sorted(lst)[-2]
    return lst[0] == second or lst[-1] == second

input()
pines = [int(x) for x in input().split()]
pine_decoration_count = sum([1 for x in range(len(pines)-2) if check_is_pine_decoration(pines[x:x + 3])])
print(pine_decoration_count)