N = int(input())
l = list(map(int, input().split()))
count = 0

for i in range(N-2):
    if l[i] == l[i+1] or l[i] == l[i+2] or l[i+1] == l[i+2]:
        continue
    if l[i] < l[i+1] < l[i+2] or l[i] > l[i+1] > l[i+2]:
        continue
    count += 1

print (count)