import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int[] nums = new int[n];
		int ans=0;

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

		for(int i=0;i<n-2;i++) {
			if(nums[i]<nums[i+1] && nums[i+1]<nums[i+2] || nums[i+2]<nums[i+1] && nums[i+1]<nums[i]) {
				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