n = int(input())
seq = input().split()

count = 0
for i in range(n - 2):
    if seq[i] == seq[i+2]:
        break
    elif seq[i] > seq[i+1] and seq[i+1] < seq[i+2]:
        count += 1
    elif seq[i] < seq[i+1] and seq[i+1] > seq[i+2]:
        count += 1
print(count)