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

count=0
for i in range(n):
    if i<2:
        continue
    else:
        x,y,z = a[i-2],a[i-1],a[i]
        if y == max(x,y,z) or y == min(x,y,z):
            if x!=y and y!=z and z!=x:
                count +=1
        
print(count)