import java.util.*;
import java.lang.Object;
public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] num = new int[n];
        int cnt = 0;
        
        for(int i = 0;i<n;i++){
            num[i] = sc.nextInt();
        }

        for(int i = 0;i<n-2;i++){
            if(num[i]<num[i+1] && num[i+1]<num[i+2]){
                cnt++;
            }else if(num[i]>num[i+1] && num[i+1]>num[i+2]){
                cnt++;
            }
        }
System.out.println(cnt);

    }
}

/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