import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		final int N = Integer.parseInt(scan.nextLine());
		final int[] array = new int[N];
		for (int i = 0; i < N; i++) {
			array[i] = Integer.parseInt(scan.next());
		}
		scan.close();

		int count = 0;
		for (int i = 0; i + 2 < N; i++) {
			if (array[i] < array[i + 1] && array[i + 1] < array[i + 2]) {
				count++;
			} else if (array[i + 2] < array[i + 1] && array[i + 1] < array[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