import java.util.*;
import java.io.*;

public class Main {
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		ArrayList<Integer> list = new ArrayList<Integer>();
		int a = sc.nextInt();
		//list.addAll(Arrays.asList(sc.nextLine()));
		for(int k = 1;k <= a; k++) {
			int j = sc.nextInt();
			list.add(j);
		}
		int count = 0;
		for (int i = 1; i < list.size()-1;i++) {
				if (list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1) || list.get(i-1) > list.get(i) && list.get(i) > list.get(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