import java.util.*;
import java.io.*;
import java.lang.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        ArrayList<Integer> arr = new ArrayList<>();
        int ans = 0;
        for (int i = 0; i<n; i++){
            int a = sc.nextInt();
            arr.add(a);
        }
        for (int i = 1; i<(n-1); i++){
            if (arr.get(i) > arr.get(i-1) && (arr.get(i) < arr.get(i+1))){
                ans++;
            }
            else if (arr.get(i) < arr.get(i-1) && (arr.get(i) > arr.get(i+1))){
                ans++;
            }
        }
        System.out.println(ans);
    }
}
/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