# coding: utf-8
# yukicoder No.116 門松列(1)

N = int(input())
A = [int(i) for i in input().split()]
count = 0

for i in range(len(A) - 2):
    kado = A[i:i + 3]
    
    if len(set(kado)) == 3: # 重複チェック
        if kado[1] == max(kado) or kado[1] == min(kado):
            count += 1

print(count)