import itertools
input()
ary = list(map(int, input().split()))
ans = 0
for i in range(len(ary) - 2):
    tmp = ary[i:i + 3]
    dup = False
    for j in itertools.combinations(tmp, 2):
        if(j[0] == j[1]):
            sup = True
    if(not dup):
        tmp[tmp.index(max(tmp))] = 0
        if(tmp.index(max(tmp)) == 0 or tmp.index(max(tmp)) == 1):
            ans += 1
print(ans)