import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
      	int a[] = new int[n];
      	int s = 0;
      	for (int i = 0; i < n; i++){
          	a[i] = sc.nextInt();
        }
        for (int i = 0; i < n-2; i++){
        	if (a[i] < a[i+1] && a[i+1] < a[i+2]){
        		s += 1;
        	}
        	if (a[i] > a[i+1] && a[i+1] > a[i+2]){
        		s += 1;
        	}
        }
        System.out.println(s);
    }
}
/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