
import java.util.Scanner;

/**
 * @author yoshizaki
 * ABC 132
 */
public class Main {
    public static void main(String[] args) {
        Scanner scanner= new Scanner(System.in);
        int len = scanner.nextInt();
        int[] numbers = new int[len];
        for(int i = 0; i < len ; i++) {
            numbers[i] = scanner.nextInt();
        }
        int answer = 0;
        for (int i = 1; i < len - 1 ; i++) {
            if(numbers[i-1] < numbers[i] && numbers[i] < numbers[i+1]) answer++;
            if(numbers[i-1] > numbers[i] && numbers[i] > numbers[i+1]) answer++;
        }
        System.out.println(answer);
    }
}
/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