N=int(input())
data=list(map(int,input().split()))
ans=0
for i in range(N-2):
    li=[data[i],data[i+1],data[i+2]]
    li_m=sorted(li)
    li_M=li_m[::-1]
    if li_m==li or li_M==li:
        continue
    elif li[0]!=li[1] and li[1]!=li[2] and li[0]!=li[2]:
        ans+=1
print(ans)