N = int(input())
A = [int(i) for i in input().split()]
t = 0
for i in range(2, N):
    if len(set(A[i-2:i+1])) == 3 and (A[i-1] == max(A[i-2:i+1]) or A[i-1] == min(A[i-2:i+1])):
            t += 1
print(t)