using System;
using System.Linq;

class Program
{
    static void Main()
    {
        int n = int.Parse(Console.ReadLine());
        int[] a = Console.ReadLine().Split().Select(int.Parse).ToArray();

        int cnt = 0;

        for (int i = 0; i < n - 2; i++)
        {
            int[] c = { a[i], a[i + 1], a[i + 2] };

            if (c[0] == c[1] || c[0] == c[2] || c[1] == c[2]) continue;

            if (c[1] == c.Max() || c[1] == c.Min()) cnt++;
        }

        Console.WriteLine(cnt);
    }
}