import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int[] p = new int[n];

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}

		int count = 0;

		for (int i = 0; i < n - 2; i++) {
			if (Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
				if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					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