using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace foryuki
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            var a = ConvertStringArrayToIntArray(Console.ReadLine().Split());
            int cnt = 0;

            for (int i = 0; i < n - 2; i++)
            {
                if (a[i] == a[i + 1] || a[i] == a[i + 2] || a[i + 1] == a[i + 2])
                {
                    continue;
                }
                if (a[i] < a[i + 1] && a[i + 1] < a[i + 2])
                {
                    continue;
                }
                if (a[i] > a[i + 1] && a[i + 1] > a[i + 2])
                {
                    continue;
                }

                cnt++;
            }

            Console.WriteLine(cnt);
        }

        //-------------------------------------------------------------

        static int[] ConvertStringArrayToIntArray(string[] array)
        {
            return Array.ConvertAll(array, str => int.Parse(str));
        }

        static List<int> ConvertStringArrayToIntList(string[] str)
        {
            var list = new List<int>();
            foreach (var c in str) list.Add(int.Parse(c));
            return list;
        }
    }
}