import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int n = scan.nextInt();
		int p[] = new int[50];
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		int ans = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i]) && (p[i] < p[i + 1])) {
				ans++;
			} else if ((p[i - 1] > p[i] && (p[i] > p[i + 1])))
				ans++;

		}

		System.out.println(ans);

	}
}
/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