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


def is_match(a, b, c) -> bool:
    if a == b or b == c or c == a: return False
    if a < b < c: return False
    if a > b > c: return False
    return True


ans = 0
for i in range(N-2):
    a, b, c = A[i], A[i+1], A[i+2]
    if is_match(a, b, c):
        ans += 1

print(ans)