import java.util.*;
public class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      int num = sc.nextInt();
      int[] array = new int[num];
      int count = 0;
      for(int i = 0;i < array.length;i++){
      	array[i] = sc.nextInt();
      }
      for(int j = 1;j < array.length-1;j++){
      	if((array[j-1] < array[j] && array[j] < array[j+1])||(array[j-1] > array[j] && array[j] > array[j+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