n = int(input())
array = list(map(int,input().split()))
count=0
for i in range(0,n-2):
    v_i = array[i:i+3]
    v = list(sorted(v_i))
    if len(list(set(v)))==3 and (v[1]==v_i[0] or v[1]==v_i[2]):
        count+=1
print(count)