import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = in.nextInt();
        }
        int ans = 0;
        for (int i = 1; i < n - 1; i++) {
            if ((p[i - 1] < p[i] && p[i] < p[i + 1]) || (p[i + 1] < p[i] && p[i] < p[i - 1])) {
                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