import sys


def input(): return sys.stdin.readline().rstrip()


def main():
    N = int(input())
    *A, = map(int, input().split())

    ans = 0
    for i in range(N-2):
        if A[i] != A[i+1] and A[i+1] != A[i+2] and A[i] != A[i+2] and \
                (A[i+1] == max(A[i:i+3]) or A[i+1] == min(A[i:i+3])):
            ans += 1

    print(ans)


if __name__ == '__main__':
    main()