import java.util.*;

public class Main{
	public static void main(String args[]){
      Scanner scan = new Scanner(System.in);
      int n = scan.nextInt();
      int[] nums = new int[n];
      int cnt = 0;
      for( int i = 0 ; i < n ; i++ ){
        nums[i] = scan.nextInt();
      }
      for( int i = 1 ; i < n-1 ; i++ ){
        if(
          (nums[i] != Math.max(nums[i],nums[i+1])) && 
          (nums[i] != Math.min(nums[i-1],nums[i])) ||
          (nums[i] != Math.max(nums[i-1],nums[i])) && 
          (nums[i] != Math.min(nums[i],nums[i+1]))     ) 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