
import java.util.Scanner;

public class Main {

	public static void main(String[] args) throws Exception {
		@SuppressWarnings("resource")
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = scanner.nextInt();
		}
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
				continue;
			}
			if (p[i + 1] < p[i] && p[i] < p[i - 1]) {
				count++;
			}
		}
		System.out.println(count);
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) throws Exception {
		@SuppressWarnings("resource")
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = scanner.nextInt();
		}
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
				continue;
			}
			if (p[i + 1] < p[i] && p[i] < p[i - 1]) {
				count++;
			}
		}
		System.out.println(count);
	}
} Main public static void main(String[] args) throws Exception {
		@SuppressWarnings("resource")
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = scanner.nextInt();
		}
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
				continue;
			}
			if (p[i + 1] < p[i] && p[i] < p[i - 1]) {
				count++;
			}
		}
		System.out.println(count);
	} main {
		@SuppressWarnings("resource")
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = scanner.nextInt();
		}
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
				continue;
			}
			if (p[i + 1] < p[i] && p[i] < p[i - 1]) {
				count++;
			}
		}
		System.out.println(count);
	} @SuppressWarnings("resource")
		Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int n = scanner.nextInt(); n scanner.nextInt() scanner.nextInt scanner int[] p = new int[n]; p new int[n] n for (int i = 0; i < n; i++) {
			p[i] = scanner.nextInt();
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			p[i] = scanner.nextInt();
		} {
			p[i] = scanner.nextInt();
		} p[i] = scanner.nextInt() p[i] p i scanner.nextInt() scanner.nextInt scanner int count = 0; count 0 for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
				continue;
			}
			if (p[i + 1] < p[i] && p[i] < p[i - 1]) {
				count++;
			}
		} 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]) {
				count++;
				continue;
			}
			if (p[i + 1] < p[i] && p[i] < p[i - 1]) {
				count++;
			}
		} {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
				continue;
			}
			if (p[i + 1] < p[i] && p[i] < p[i - 1]) {
				count++;
			}
		} if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
				continue;
			} 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 {
				count++;
				continue;
			} count++ count continue; if (p[i + 1] < p[i] && p[i] < p[i - 1]) {
				count++;
			} 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 {
				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) throws Exception {
		@SuppressWarnings("resource")
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = scanner.nextInt();
		}
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
				continue;
			}
			if (p[i + 1] < p[i] && p[i] < p[i - 1]) {
				count++;
			}
		}
		System.out.println(count);
	}
} public class Main {

	public static void main(String[] args) throws Exception {
		@SuppressWarnings("resource")
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = scanner.nextInt();
		}
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
				continue;
			}
			if (p[i + 1] < p[i] && p[i] < p[i - 1]) {
				count++;
			}
		}
		System.out.println(count);
	}
} Main

import java.util.Scanner;

public class Main {

	public static void main(String[] args) throws Exception {
		@SuppressWarnings("resource")
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = scanner.nextInt();
		}
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
				continue;
			}
			if (p[i + 1] < p[i] && p[i] < p[i - 1]) {
				count++;
			}
		}
		System.out.println(count);
	}
}
