import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] p = new int[n];
    for (int i = 0; i < n; i++) {
      p[i] = Integer.parseInt(sc.next());
    }

    int cnt = 0;
    for (int i = 1; i < n - 1; i++) {
      if (Math.min(p[i - 1], p[i]) == p[i]) {
        if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        }
      } else {
        if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        }
      }
    }
    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