using System;
using System.Collections.Generic;
using System.Linq;

class Magatro
{
    static void Main()
    {
        int N = int.Parse(Console.ReadLine());
        int cnt = 0;
        int[]A = Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();
        for(int i = 1; i < N-1; i++)
        {
            if (A[i - 1] != A[i] && A[i - 1] != A[i + 1] && A[i] != A[i + 1])
            {
                int[] arr = new int[3];
                arr[0] = A[i - 1];
                arr[1] = A[i];
                arr[2] = A[i + 1];
                if (arr[1] == arr.Max()||arr[1]==arr.Min())
                {
                    cnt++;
                }
            }
        }
        Console.WriteLine(cnt);
    }
}