import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int[] array = new int[a];
		int count = 0;
		for(int i = 0; i < a; i++) {
			array[i] = sc.nextInt();
		}
		for(int i = 1; i < array.length - 1; i++) {
			if(array[i -1] < array[i] && array[i] < array[i + 1]) {
				count++;
			}else if(array[i + 1] < array[i] && array[i] < array[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 a = sc.nextInt();
		int[] array = new int[a];
		int count = 0;
		for(int i = 0; i < a; i++) {
			array[i] = sc.nextInt();
		}
		for(int i = 1; i < array.length - 1; i++) {
			if(array[i -1] < array[i] && array[i] < array[i + 1]) {
				count++;
			}else if(array[i + 1] < array[i] && array[i] < array[i - 1]) {
				count++;
			}
		}
		System.out.println(count);
	}
} Main public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int[] array = new int[a];
		int count = 0;
		for(int i = 0; i < a; i++) {
			array[i] = sc.nextInt();
		}
		for(int i = 1; i < array.length - 1; i++) {
			if(array[i -1] < array[i] && array[i] < array[i + 1]) {
				count++;
			}else if(array[i + 1] < array[i] && array[i] < array[i - 1]) {
				count++;
			}
		}
		System.out.println(count);
	} main {
		
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int[] array = new int[a];
		int count = 0;
		for(int i = 0; i < a; i++) {
			array[i] = sc.nextInt();
		}
		for(int i = 1; i < array.length - 1; i++) {
			if(array[i -1] < array[i] && array[i] < array[i + 1]) {
				count++;
			}else if(array[i + 1] < array[i] && array[i] < array[i - 1]) {
				count++;
			}
		}
		System.out.println(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc int[] array = new int[a]; array new int[a] a int count = 0; count 0 for(int i = 0; i < a; i++) {
			array[i] = sc.nextInt();
		} int i = 0; int i = 0; i 0 i < a i a i++ i++ i {
			array[i] = sc.nextInt();
		} {
			array[i] = sc.nextInt();
		} array[i] = sc.nextInt() array[i] array i sc.nextInt() sc.nextInt sc for(int i = 1; i < array.length - 1; i++) {
			if(array[i -1] < array[i] && array[i] < array[i + 1]) {
				count++;
			}else if(array[i + 1] < array[i] && array[i] < array[i - 1]) {
				count++;
			}
		} int i = 1; int i = 1; i 1 i < array.length - 1 i array.length - 1 array.length array array.length 1 i++ i++ i {
			if(array[i -1] < array[i] && array[i] < array[i + 1]) {
				count++;
			}else if(array[i + 1] < array[i] && array[i] < array[i - 1]) {
				count++;
			}
		} {
			if(array[i -1] < array[i] && array[i] < array[i + 1]) {
				count++;
			}else if(array[i + 1] < array[i] && array[i] < array[i - 1]) {
				count++;
			}
		} if(array[i -1] < array[i] && array[i] < array[i + 1]) {
				count++;
			}else if(array[i + 1] < array[i] && array[i] < array[i - 1]) {
				count++;
			} array[i -1] < array[i] && array[i] < array[i + 1] array[i -1] < array[i] array[i -1] array i -1 i 1 array[i] array i array[i] < array[i + 1] array[i] array i array[i + 1] array i + 1 i 1 {
				count++;
			} count++ count if(array[i + 1] < array[i] && array[i] < array[i - 1]) {
				count++;
			} array[i + 1] < array[i] && array[i] < array[i - 1] array[i + 1] < array[i] array[i + 1] array i + 1 i 1 array[i] array i array[i] < array[i - 1] array[i] array i array[i - 1] array 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 a = sc.nextInt();
		int[] array = new int[a];
		int count = 0;
		for(int i = 0; i < a; i++) {
			array[i] = sc.nextInt();
		}
		for(int i = 1; i < array.length - 1; i++) {
			if(array[i -1] < array[i] && array[i] < array[i + 1]) {
				count++;
			}else if(array[i + 1] < array[i] && array[i] < array[i - 1]) {
				count++;
			}
		}
		System.out.println(count);
	}
} public class Main {

	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int[] array = new int[a];
		int count = 0;
		for(int i = 0; i < a; i++) {
			array[i] = sc.nextInt();
		}
		for(int i = 1; i < array.length - 1; i++) {
			if(array[i -1] < array[i] && array[i] < array[i + 1]) {
				count++;
			}else if(array[i + 1] < array[i] && array[i] < array[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 a = sc.nextInt();
		int[] array = new int[a];
		int count = 0;
		for(int i = 0; i < a; i++) {
			array[i] = sc.nextInt();
		}
		for(int i = 1; i < array.length - 1; i++) {
			if(array[i -1] < array[i] && array[i] < array[i + 1]) {
				count++;
			}else if(array[i + 1] < array[i] && array[i] < array[i - 1]) {
				count++;
			}
		}
		System.out.println(count);
	}
}