n=int(input())
l=list(map(int,input().split()))
cnt=0
for i in range(n-2):
    if(l[i]!=l[i+1] and l[i]!=l[i+2] and l[i+1]!=l[i+2] and not (l[i+2]>l[i+1]>l[i] or l[i+2]<l[i+1]<l[i])):
        cnt+=1
print(cnt)