# -*- coding:utf-8 -*-

matsuCount = int(input())
matsuList = [int(i) for i in input().rstrip().split(" ")]

ans = 0
for i in range(matsuCount - 2):
    subList = matsuList[i:i+3]
    if len(set(subList)) != 3:
        continue
    if max(subList) == subList[1]:
        ans += 1
    elif min(subList) == subList[1]:
        ans += 1

print(ans)