import java.util.Arrays;
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[] a = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		int[] b = new int[3];

		int count = 0;

		for (int i = 1; i < n - 1; i++) {
			b[0] = a[i - 1];
			b[1] = a[i];
			b[2] = a[i + 1];
			Arrays.sort(b);
			if (b[1] == a[i])
				count++;
		}
		System.out.println(count);
	}

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

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int[] a = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		int[] b = new int[3];

		int count = 0;

		for (int i = 1; i < n - 1; i++) {
			b[0] = a[i - 1];
			b[1] = a[i];
			b[2] = a[i + 1];
			Arrays.sort(b);
			if (b[1] == a[i])
				count++;
		}
		System.out.println(count);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int[] a = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		int[] b = new int[3];

		int count = 0;

		for (int i = 1; i < n - 1; i++) {
			b[0] = a[i - 1];
			b[1] = a[i];
			b[2] = a[i + 1];
			Arrays.sort(b);
			if (b[1] == a[i])
				count++;
		}
		System.out.println(count);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int[] a = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		int[] b = new int[3];

		int count = 0;

		for (int i = 1; i < n - 1; i++) {
			b[0] = a[i - 1];
			b[1] = a[i];
			b[2] = a[i + 1];
			Arrays.sort(b);
			if (b[1] == a[i])
				count++;
		}
		System.out.println(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = Integer.parseInt(sc.next()); n Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int[] a = new int[n]; a new int[n] n for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sc.next());
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			a[i] = Integer.parseInt(sc.next());
		} {
			a[i] = Integer.parseInt(sc.next());
		} a[i] = Integer.parseInt(sc.next()) a[i] a i Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int[] b = new int[3]; b new int[3] 3 int count = 0; count 0 for (int i = 1; i < n - 1; i++) {
			b[0] = a[i - 1];
			b[1] = a[i];
			b[2] = a[i + 1];
			Arrays.sort(b);
			if (b[1] == a[i])
				count++;
		} int i = 1; int i = 1; i 1 i < n - 1 i n - 1 n 1 i++ i++ i {
			b[0] = a[i - 1];
			b[1] = a[i];
			b[2] = a[i + 1];
			Arrays.sort(b);
			if (b[1] == a[i])
				count++;
		} {
			b[0] = a[i - 1];
			b[1] = a[i];
			b[2] = a[i + 1];
			Arrays.sort(b);
			if (b[1] == a[i])
				count++;
		} b[0] = a[i - 1] b[0] b 0 a[i - 1] a i - 1 i 1 b[1] = a[i] b[1] b 1 a[i] a i b[2] = a[i + 1] b[2] b 2 a[i + 1] a i + 1 i 1 Arrays.sort(b) Arrays.sort Arrays b if (b[1] == a[i])
				count++; b[1] == a[i] b[1] b 1 a[i] a i count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int[] a = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		int[] b = new int[3];

		int count = 0;

		for (int i = 1; i < n - 1; i++) {
			b[0] = a[i - 1];
			b[1] = a[i];
			b[2] = a[i + 1];
			Arrays.sort(b);
			if (b[1] == a[i])
				count++;
		}
		System.out.println(count);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int[] a = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		int[] b = new int[3];

		int count = 0;

		for (int i = 1; i < n - 1; i++) {
			b[0] = a[i - 1];
			b[1] = a[i];
			b[2] = a[i + 1];
			Arrays.sort(b);
			if (b[1] == a[i])
				count++;
		}
		System.out.println(count);
	}

} Main
import java.util.Arrays;
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[] a = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sc.next());
		}
		int[] b = new int[3];

		int count = 0;

		for (int i = 1; i < n - 1; i++) {
			b[0] = a[i - 1];
			b[1] = a[i];
			b[2] = a[i + 1];
			Arrays.sort(b);
			if (b[1] == a[i])
				count++;
		}
		System.out.println(count);
	}

}
