n=int(input())
a=list(map(int,input().split()))
cnt = 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

    cnt+=1
    
print(cnt)