import java.util.Scanner;

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