from typing import Sequence


def is_kadomatsu(height_seq: Sequence[int]) -> bool:
    if len(set(height_seq)) != 3:
        return False

    if max(height_seq) == height_seq[1] or min(height_seq) == height_seq[1]:
        return True
    return False


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

    ctr = 0
    for idx in range(N-2):
        if is_kadomatsu(A[idx:idx+3]):
            ctr += 1

    print(ctr)


if __name__ == "__main__":
    main()