import java.util.List;
import java.util.ArrayList;
import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    List<Integer> list = new ArrayList<Integer>();
    int n = sc.nextInt();
    for (int i = 0; i < n; i++)
	  list.add(sc.nextInt());
    int count = 0;
    for (int i = 1; i < n - 1; i++)
      if ((list.get(i-1) > list.get(i) && list.get(i) > list.get(i+1)) || list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1))
        count++;
    System.out.print(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