import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        int[] nums = new int[n];
        int count = 0;
        for (int i = 0; i < n; i++) {
            nums[i] = sc.nextInt();
            if(i>=2){
                if( (nums[i-2] <nums[i-1] && nums[i-1] <=nums[i]) ||
                        (nums[i] <nums[i-1] && nums[i-1] <=nums[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