N = int(input())
ans = 0
A = list(map(int, input().split()))
for i in range(N - 2):
    a, b, c = A[i: i + 3]
    if a == b or b == c or c == a:
        continue
    if b == min(a, b, c) or b == max(a, b, c):
        ans += 1
print(ans)