
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 ans = 0;
		for(int i = 0 ; i < n ; i++) {
			if(i >= 1 && i < n - 1) {
				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);
		sc.close();

	}

}

/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