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

def is_kadomatu(x,y,z):
    if x == y or y==z or z==x: return 0
    return 1 if y == max(x,y,z) or y == min(x,y,z) else 0

print(sum(is_kadomatu(a[i],a[i+1],a[i+2]) for i in range(n-2)))