import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int n = scan.nextInt();
		int p[] = new int[50];
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		int ans = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i]) && (p[i] < p[i + 1])) {
				ans++;
			} else if ((p[i - 1] > p[i] && (p[i] > p[i + 1])))
				ans++;

		}

		System.out.println(ans);

	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int n = scan.nextInt();
		int p[] = new int[50];
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		int ans = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i]) && (p[i] < p[i + 1])) {
				ans++;
			} else if ((p[i - 1] > p[i] && (p[i] > p[i + 1])))
				ans++;

		}

		System.out.println(ans);

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

		Scanner scan = new Scanner(System.in);

		int n = scan.nextInt();
		int p[] = new int[50];
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		int ans = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i]) && (p[i] < p[i + 1])) {
				ans++;
			} else if ((p[i - 1] > p[i] && (p[i] > p[i + 1])))
				ans++;

		}

		System.out.println(ans);

	} main {

		Scanner scan = new Scanner(System.in);

		int n = scan.nextInt();
		int p[] = new int[50];
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		int ans = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i]) && (p[i] < p[i + 1])) {
				ans++;
			} else if ((p[i - 1] > p[i] && (p[i] > p[i + 1])))
				ans++;

		}

		System.out.println(ans);

	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int n = scan.nextInt(); n scan.nextInt() scan.nextInt scan int p[] = new int[50]; p new int[50] 50 for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			p[i] = scan.nextInt();
		} {
			p[i] = scan.nextInt();
		} p[i] = scan.nextInt() p[i] p i scan.nextInt() scan.nextInt scan int ans = 0; ans 0 for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i]) && (p[i] < p[i + 1])) {
				ans++;
			} else if ((p[i - 1] > p[i] && (p[i] > p[i + 1])))
				ans++;

		} int i = 1; int i = 1; i 1 i < n - 1 i n - 1 n 1 i++ i++ i {
			if ((p[i - 1] < p[i]) && (p[i] < p[i + 1])) {
				ans++;
			} else if ((p[i - 1] > p[i] && (p[i] > p[i + 1])))
				ans++;

		} {
			if ((p[i - 1] < p[i]) && (p[i] < p[i + 1])) {
				ans++;
			} else if ((p[i - 1] > p[i] && (p[i] > p[i + 1])))
				ans++;

		} if ((p[i - 1] < p[i]) && (p[i] < p[i + 1])) {
				ans++;
			} else if ((p[i - 1] > p[i] && (p[i] > p[i + 1])))
				ans++; (p[i - 1] < p[i]) && (p[i] < p[i + 1]) (p[i - 1] < p[i]) p[i - 1] p i - 1 i 1 p[i] p i (p[i] < p[i + 1]) p[i] p i p[i + 1] p i + 1 i 1 {
				ans++;
			} ans++ ans if ((p[i - 1] > p[i] && (p[i] > p[i + 1])))
				ans++; (p[i - 1] > p[i] && (p[i] > p[i + 1])) p[i - 1] > p[i] p[i - 1] p i - 1 i 1 p[i] p i (p[i] > p[i + 1]) p[i] p i p[i + 1] p i + 1 i 1 ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int n = scan.nextInt();
		int p[] = new int[50];
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		int ans = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i]) && (p[i] < p[i + 1])) {
				ans++;
			} else if ((p[i - 1] > p[i] && (p[i] > p[i + 1])))
				ans++;

		}

		System.out.println(ans);

	}
} public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int n = scan.nextInt();
		int p[] = new int[50];
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		int ans = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i]) && (p[i] < p[i + 1])) {
				ans++;
			} else if ((p[i - 1] > p[i] && (p[i] > p[i + 1])))
				ans++;

		}

		System.out.println(ans);

	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int n = scan.nextInt();
		int p[] = new int[50];
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		int ans = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i]) && (p[i] < p[i + 1])) {
				ans++;
			} else if ((p[i - 1] > p[i] && (p[i] > p[i + 1])))
				ans++;

		}

		System.out.println(ans);

	}
}