class Program
{
    static void Main(string[] args)
    {
        int totall = int.Parse(Console.ReadLine()!);
        string[] nums = Console.ReadLine()!.Split(' ');
        List<int> numList = new List<int>();
        int count = 0;

        for (int i = 0; i < nums.Length; i++)
        {
            numList.Add(int.Parse(nums[i]));
        }

        for (int i = 0; i < numList.Count - 2; i++)
        {
            if (numList[i] != numList[i + 1] && numList[i + 1] != numList[i + 2]
                && numList[i] != numList[i + 2])
            {
                if (numList[i + 1] > numList[i] && numList[i + 1] > numList[i + 2]
                    || numList[i + 1] < numList[i] && numList[i + 1] < numList[i + 2])
                {
                    count++;
                }
            }
        }

        Console.WriteLine(count);
    }
}