import sequtils,strutils

var
    N = stdin.readline.parseInt
    A = stdin.readline.split.map(parseInt)
    cnt : int

for i in 0..<N - 2:
    if A[i] < A[i + 1] and A[i + 2] < A[i + 1] and A[i + 2] != A[i]:
        cnt += 1
    elif A[i] > A[i + 1] and A[i + 2] > A[i + 1] and A[i + 2] != A[i]:
        cnt += 1

echo cnt