import java.util.Scanner;

public class Main {
	public static void main(String[] args) {

		try {
			Scanner scan = new Scanner(System.in);
			int count = scan.nextInt();

			int[] height = new int[count];
			for (int i = 0; i < count; ++i) {
				height[i] = scan.nextInt();
			}

			int ans = 0;
			for (int i = 1; i < count - 1; ++i) {
				int max = 0, min = 101;
				boolean flag = false;
				for (int j = -1; j < 2; ++j) {
					if (max == height[i + j] || min == height[i + j]) {
						flag = true;
						break;
					}
					if (max < height[i + j]) {
						max = height[i + j];
					}
					if (min > height[i + j]) {
						min = height[i + j];
					}
				}
				if (flag) {
					continue;
				}
				if (max != height[i - 1] && min != height[i - 1] || max != height[i + 1] && min != height[i + 1]) {
					++ans;
				}
			}

			System.out.println(ans);
			scan.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}