import java.util.ArrayList;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        ArrayList<Integer> arrayList = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            arrayList.add(scanner.nextInt());
        }
        int cnt = 0;
        for (int i = 1; i < n-1; i++) {
            if(arrayList.get(i-1) < arrayList.get(i) && arrayList.get(i) < arrayList.get(i+1) ||
                arrayList.get(i+1) < arrayList.get(i) && arrayList.get(i) < arrayList.get(i-1)) cnt++;
        }
        System.out.println(cnt);
    }
}

/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