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];
		int count=0;
		
		for(int i=0;i<n;i++) {
			p[i]=sc.nextInt();
		}
		
		for(int i=0;i<(n-2);i++) {
			
			if((p[i]<p[i+1]&&p[i+1]<p[i+2])||p[i+2]<p[i+1]&&p[i+1]<p[i]||(p[i]<p[i+1]&&p[i+1]==p[i+2])||p[i+2]<p[i+1]&&p[i+1]==p[i]) {
				count+=1;
			}
		}
		
		System.out.println(count);
		
		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