import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		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 count = 0;

		for (int i = 0; i < n - 2; i++) {
			if (Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
				if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					count++;
				}
			}
		}

		System.out.println(count);
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {

		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 count = 0;

		for (int i = 0; i < n - 2; i++) {
			if (Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
				if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					count++;
				}
			}
		}

		System.out.println(count);
	}
} Main public static void main(String[] args) {

		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 count = 0;

		for (int i = 0; i < n - 2; i++) {
			if (Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
				if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					count++;
				}
			}
		}

		System.out.println(count);
	} main {

		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 count = 0;

		for (int i = 0; i < n - 2; i++) {
			if (Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
				if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					count++;
				}
			}
		}

		System.out.println(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] p = new int[n]; p new int[n] n for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			p[i] = sc.nextInt();
		} {
			p[i] = sc.nextInt();
		} p[i] = sc.nextInt() p[i] p i sc.nextInt() sc.nextInt sc int count = 0; count 0 for (int i = 0; i < n - 2; i++) {
			if (Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
				if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					count++;
				}
			}
		} int i = 0; int i = 0; i 0 i < n - 2 i n - 2 n 2 i++ i++ i {
			if (Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
				if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					count++;
				}
			}
		} {
			if (Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
				if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					count++;
				}
			}
		} if (Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
				if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					count++;
				}
			} Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) != p[i + 1] Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) Math.max Math Math.max(p[i], p[i + 1]) Math.max Math p[i] p i p[i + 1] p i + 1 i 1 p[i + 2] p i + 2 i 2 p[i + 1] p i + 1 i 1 {
				if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					count++;
				}
			} if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					count++;
				} Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1] Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) Math.min Math Math.min(p[i], p[i + 1]) Math.min Math p[i] p i p[i + 1] p i + 1 i 1 p[i + 2] p i + 2 i 2 p[i + 1] p i + 1 i 1 {
					count++;
				} 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 = sc.nextInt();
		int[] p = new int[n];

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}

		int count = 0;

		for (int i = 0; i < n - 2; i++) {
			if (Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
				if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					count++;
				}
			}
		}

		System.out.println(count);
	}
} public class Main {

	public static void main(String[] args) {

		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 count = 0;

		for (int i = 0; i < n - 2; i++) {
			if (Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
				if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					count++;
				}
			}
		}

		System.out.println(count);
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		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 count = 0;

		for (int i = 0; i < n - 2; i++) {
			if (Math.max(Math.max(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
				if (Math.min(Math.min(p[i], p[i + 1]), p[i + 2]) != p[i + 1]) {
					count++;
				}
			}
		}

		System.out.println(count);
	}
}