import java.util.*;

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 count = 0;

    for(int i=0; i < N; i++){
        num[i] = sc.nextInt();
        if(i > 1){
            if(num[i-2] > num[i-1] && num[i-1] > num[i]){
                count++;
            }else if(num[i-2] < num[i-1] && num[i-1] < num[i]){
                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