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

length = len(a)
start = 0
end = start+2

res = 0

while end < length:
    cur = a[start:end+1]
    
    cur_sorted = sorted(cur, reverse=True)
    if cur_sorted[1] == cur[0] or cur_sorted[1] == cur[2]:
        if cur_sorted[0] != cur_sorted[1] and cur_sorted[1] != cur_sorted[2]:
            res += 1
        
    start += 1
    end = start+2
    
print(res)