N = int(input())
A = list(map(int,input().split()))
COUNT = 0
for I in range(N - 2):
    if len({A[I], A[I + 1], A[I + 2]}) < 3:
        continue
    if A[I] < A[I + 1] < A[I + 2] or a[I] > a[I + 1] > a[I + 2]:
        continue
    COUNT += 1
print(COUNT)