cnt = int(input())

matsu_list = list(map(int, input().split(' ')))

output = 0

for i in range(cnt - 2):
    kadoMatsu_list = []
    for j in range(3):
        kadoMatsu_list.append(matsu_list[i + j])
    if len(set(kadoMatsu_list)) == 3:
        if kadoMatsu_list[0] < kadoMatsu_list[1] and kadoMatsu_list[2] < kadoMatsu_list[1] or\
                kadoMatsu_list[1] < kadoMatsu_list[0] and kadoMatsu_list[1] < kadoMatsu_list[2]:
            output += 1

print(output)