n=int(input())
a=list(map(int,input().split()))
cnt=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 max(a[i],a[i+1],a[i+2])==a[i+1] or min(a[i],a[i+1],a[i+2])==a[i+1]:
        cnt+=1
print(cnt)