N = int(input())
A = list(map(int,input().split()))
ans = 0
for i in range(N-2):
    if A[i] == A[i+1] or A[i] == A[i+2] or A[i+1] == A[i+2]:
        continue
    if A[i] < A[i+1] < A[i+2] or A[i] > A[i+1] > A[i+2]:
        continue
    ans += 1
print(ans)