import java.util.Scanner;

public class Main {

    public static void main(String args[]) {

        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        Integer[] p = new Integer[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int result = 0;
        for (int i = 1; i < n - 1; i++) {
            if (Math.max(p[i-1], p[i+1]) >= p[i] && Math.min(p[i-1], p[i+1]) <= p[i]) {
                result++;
            }
        }

        System.out.println(result);
    }
}

/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