  import java.util.*;
  public class Main {
      public static void main(String[] args){
          Scanner sc = new Scanner(System.in);
          int n = sc.nextInt();
          int a,b,c;
          a = sc.nextInt();
          b = sc.nextInt();
          c = sc.nextInt();
          int count = 0;
          if((a<b&&b<c)||(c<b&&b<a)){
          count ++;}
          for(int i=0;i<n-3;i++){
          a = b;
          b = c;
          c = sc.nextInt();
          if((a<b&&b<c)||(c<b&&b<a)){
          count ++;}
          }
          
          
          
          System.out.println(count);
          
          sc.close();
          }
          }
/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