import java.util.*;

public class Main {
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int[] ar = new int[N];
        for (int i = 0; i < N; i++) {
            ar[i] = sc.nextInt();
        }
        int count = 0;
        for (int i = 0; i < N-2; i++) {
            int max = Math.max(Math.max(ar[i], ar[i+1]), ar[i+2]);
            int min = Math.min(Math.min(ar[i], ar[i+1]), ar[i+2]);
            if (ar[i+1] != max && ar[i+1] != min) {
                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