import java.util.*;

public class Main{

    public static void main(String args[]){

        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        int p[] = new int[n];

        for (int i=0; i<n; i++){
            p[i] = sc.nextInt();
        }

        int count=0;

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