n = int(input())
s = list(map(int, input().strip().split()))
cnt=0
for i in range(n-2):
    if len(set(s[i:i+3]))==3:
        if s[i] > s[i+1] < s[i+2] or s[i] < s[i+1] > s[i+2]:
            cnt+=1
print(cnt)