import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] nums = new int[n];
		for(int i =0; i< n; i++) {
			nums[i] = sc.nextInt();
		}
		int cnt =0;
		for(int i = 0; i < nums.length - 2; i++) {
			if(nums[i+1] > nums[i] && nums[i+2] > nums[i+1] ) {
				cnt++;
			}else if(nums[i+1] < nums[i] && nums[i+2] < nums[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}

} 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[] nums = new int[n];
		for(int i =0; i< n; i++) {
			nums[i] = sc.nextInt();
		}
		int cnt =0;
		for(int i = 0; i < nums.length - 2; i++) {
			if(nums[i+1] > nums[i] && nums[i+2] > nums[i+1] ) {
				cnt++;
			}else if(nums[i+1] < nums[i] && nums[i+2] < nums[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] nums = new int[n];
		for(int i =0; i< n; i++) {
			nums[i] = sc.nextInt();
		}
		int cnt =0;
		for(int i = 0; i < nums.length - 2; i++) {
			if(nums[i+1] > nums[i] && nums[i+2] > nums[i+1] ) {
				cnt++;
			}else if(nums[i+1] < nums[i] && nums[i+2] < nums[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] nums = new int[n];
		for(int i =0; i< n; i++) {
			nums[i] = sc.nextInt();
		}
		int cnt =0;
		for(int i = 0; i < nums.length - 2; i++) {
			if(nums[i+1] > nums[i] && nums[i+2] > nums[i+1] ) {
				cnt++;
			}else if(nums[i+1] < nums[i] && nums[i+2] < nums[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] nums = new int[n]; nums new int[n] n for(int i =0; i< n; i++) {
			nums[i] = sc.nextInt();
		} int i =0; int i =0; i 0 i< n i n i++ i++ i {
			nums[i] = sc.nextInt();
		} {
			nums[i] = sc.nextInt();
		} nums[i] = sc.nextInt() nums[i] nums i sc.nextInt() sc.nextInt sc int cnt =0; cnt 0 for(int i = 0; i < nums.length - 2; i++) {
			if(nums[i+1] > nums[i] && nums[i+2] > nums[i+1] ) {
				cnt++;
			}else if(nums[i+1] < nums[i] && nums[i+2] < nums[i+1]) {
				cnt++;
			}
		} int i = 0; int i = 0; i 0 i < nums.length - 2 i nums.length - 2 nums.length nums nums.length 2 i++ i++ i {
			if(nums[i+1] > nums[i] && nums[i+2] > nums[i+1] ) {
				cnt++;
			}else if(nums[i+1] < nums[i] && nums[i+2] < nums[i+1]) {
				cnt++;
			}
		} {
			if(nums[i+1] > nums[i] && nums[i+2] > nums[i+1] ) {
				cnt++;
			}else if(nums[i+1] < nums[i] && nums[i+2] < nums[i+1]) {
				cnt++;
			}
		} if(nums[i+1] > nums[i] && nums[i+2] > nums[i+1] ) {
				cnt++;
			}else if(nums[i+1] < nums[i] && nums[i+2] < nums[i+1]) {
				cnt++;
			} nums[i+1] > nums[i] && nums[i+2] > nums[i+1] nums[i+1] > nums[i] nums[i+1] nums i+1 i 1 nums[i] nums i nums[i+2] > nums[i+1] nums[i+2] nums i+2 i 2 nums[i+1] nums i+1 i 1 {
				cnt++;
			} cnt++ cnt if(nums[i+1] < nums[i] && nums[i+2] < nums[i+1]) {
				cnt++;
			} nums[i+1] < nums[i] && nums[i+2] < nums[i+1] nums[i+1] < nums[i] nums[i+1] nums i+1 i 1 nums[i] nums i nums[i+2] < nums[i+1] nums[i+2] nums i+2 i 2 nums[i+1] nums i+1 i 1 {
				cnt++;
			} cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] nums = new int[n];
		for(int i =0; i< n; i++) {
			nums[i] = sc.nextInt();
		}
		int cnt =0;
		for(int i = 0; i < nums.length - 2; i++) {
			if(nums[i+1] > nums[i] && nums[i+2] > nums[i+1] ) {
				cnt++;
			}else if(nums[i+1] < nums[i] && nums[i+2] < nums[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}

} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] nums = new int[n];
		for(int i =0; i< n; i++) {
			nums[i] = sc.nextInt();
		}
		int cnt =0;
		for(int i = 0; i < nums.length - 2; i++) {
			if(nums[i+1] > nums[i] && nums[i+2] > nums[i+1] ) {
				cnt++;
			}else if(nums[i+1] < nums[i] && nums[i+2] < nums[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}

} 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[] nums = new int[n];
		for(int i =0; i< n; i++) {
			nums[i] = sc.nextInt();
		}
		int cnt =0;
		for(int i = 0; i < nums.length - 2; i++) {
			if(nums[i+1] > nums[i] && nums[i+2] > nums[i+1] ) {
				cnt++;
			}else if(nums[i+1] < nums[i] && nums[i+2] < nums[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}

}
