N = int(input())
A = list(map(int, input().split()))

count = 0
for i in range(3, N + 1):
    k = A[i-3:i]
    sk = sorted(k)
    if k.index(sk[1]) % 2 == 0 and len(set(k)) == len(k):
        count += 1
print(count)