N = int(input())
A = [int(x) for x in input().split()]


def isKadomatsu(arr):
    if len(arr) != len(set(arr)):
        return False

    i = arr.index(sorted(arr)[1])
    if i == 1:
        return False
    else:
        return True


ans = 0
for i in range(N - 2):
    if isKadomatsu(A[i:i + 3]):
        ans += 1
print(ans)