//created by Whiplash99
import java.io.*;
import java.util.*;
public class Main
{
    public static void main(String[] args) throws IOException
    {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

        int i,N;

        N=Integer.parseInt(br.readLine().trim());
        String s[]=br.readLine().trim().split(" ");
        int a[]=new int[N];
        for(i=0;i<N;i++) a[i]=Integer.parseInt(s[i]);

        int count=0;
        for(i=1;i<N-1;i++)
        {
            if(a[i]<=a[i-1]&&a[i]>=a[i+1]) count++;
            else if(a[i]>=a[i-1]&&a[i]<=a[i+1]) count++;
        }
        System.out.println(count);
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz