import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int n = Integer.parseInt(sc.next());
		int[] p = new int[n];
		int idx;
		for (idx = 0; idx < n; idx++) {
			p[idx] = Integer.parseInt(sc.next());
		}

		int cnt = 0;
		for (idx = 1; idx < n - 1; idx++) {
			if (p[idx] <= p[idx - 1]) {
				if (p[idx] > p[idx + 1]) {
					++cnt;
				}
			} else { //if (p[idx] > p[idx -1]) {
				if (p[idx] <= p[idx + 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