import java.util.Scanner;

public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] p = new int[n];
		
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		
		int[] three = new int[3];
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			three[0] = p[i - 1];
			three[1] = p[i];
			three[2] = p[i + 1];
			
			if (three[1] >= three[0] && three[1] < three[2]) count++;
			if(three[1] < three[0] && three[1] >= three[2]) count++;
		}
		
		System.out.println(count);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] p = new int[n];
		
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		
		int[] three = new int[3];
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			three[0] = p[i - 1];
			three[1] = p[i];
			three[2] = p[i + 1];
			
			if (three[1] >= three[0] && three[1] < three[2]) count++;
			if(three[1] < three[0] && three[1] >= three[2]) count++;
		}
		
		System.out.println(count);
	}
} Main public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] p = new int[n];
		
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		
		int[] three = new int[3];
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			three[0] = p[i - 1];
			three[1] = p[i];
			three[2] = p[i + 1];
			
			if (three[1] >= three[0] && three[1] < three[2]) count++;
			if(three[1] < three[0] && three[1] >= three[2]) count++;
		}
		
		System.out.println(count);
	} main {

		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] p = new int[n];
		
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		
		int[] three = new int[3];
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			three[0] = p[i - 1];
			three[1] = p[i];
			three[2] = p[i + 1];
			
			if (three[1] >= three[0] && three[1] < three[2]) count++;
			if(three[1] < three[0] && three[1] >= three[2]) count++;
		}
		
		System.out.println(count);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int n = scan.nextInt(); n scan.nextInt() scan.nextInt scan int[] p = new int[n]; p new int[n] n for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			p[i] = scan.nextInt();
		} {
			p[i] = scan.nextInt();
		} p[i] = scan.nextInt() p[i] p i scan.nextInt() scan.nextInt scan int[] three = new int[3]; three new int[3] 3 int count = 0; count 0 for (int i = 1; i < n - 1; i++) {
			three[0] = p[i - 1];
			three[1] = p[i];
			three[2] = p[i + 1];
			
			if (three[1] >= three[0] && three[1] < three[2]) count++;
			if(three[1] < three[0] && three[1] >= three[2]) count++;
		} int i = 1; int i = 1; i 1 i < n - 1 i n - 1 n 1 i++ i++ i {
			three[0] = p[i - 1];
			three[1] = p[i];
			three[2] = p[i + 1];
			
			if (three[1] >= three[0] && three[1] < three[2]) count++;
			if(three[1] < three[0] && three[1] >= three[2]) count++;
		} {
			three[0] = p[i - 1];
			three[1] = p[i];
			three[2] = p[i + 1];
			
			if (three[1] >= three[0] && three[1] < three[2]) count++;
			if(three[1] < three[0] && three[1] >= three[2]) count++;
		} three[0] = p[i - 1] three[0] three 0 p[i - 1] p i - 1 i 1 three[1] = p[i] three[1] three 1 p[i] p i three[2] = p[i + 1] three[2] three 2 p[i + 1] p i + 1 i 1 if (three[1] >= three[0] && three[1] < three[2]) count++; three[1] >= three[0] && three[1] < three[2] three[1] >= three[0] three[1] three 1 three[0] three 0 three[1] < three[2] three[1] three 1 three[2] three 2 count++ count if(three[1] < three[0] && three[1] >= three[2]) count++; three[1] < three[0] && three[1] >= three[2] three[1] < three[0] three[1] three 1 three[0] three 0 three[1] >= three[2] three[1] three 1 three[2] three 2 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 scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] p = new int[n];
		
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		
		int[] three = new int[3];
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			three[0] = p[i - 1];
			three[1] = p[i];
			three[2] = p[i + 1];
			
			if (three[1] >= three[0] && three[1] < three[2]) count++;
			if(three[1] < three[0] && three[1] >= three[2]) count++;
		}
		
		System.out.println(count);
	}
} public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] p = new int[n];
		
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		
		int[] three = new int[3];
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			three[0] = p[i - 1];
			three[1] = p[i];
			three[2] = p[i + 1];
			
			if (three[1] >= three[0] && three[1] < three[2]) count++;
			if(three[1] < three[0] && three[1] >= three[2]) count++;
		}
		
		System.out.println(count);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] p = new int[n];
		
		for (int i = 0; i < n; i++) {
			p[i] = scan.nextInt();
		}
		
		int[] three = new int[3];
		int count = 0;
		for (int i = 1; i < n - 1; i++) {
			three[0] = p[i - 1];
			three[1] = p[i];
			three[2] = p[i + 1];
			
			if (three[1] >= three[0] && three[1] < three[2]) count++;
			if(three[1] < three[0] && three[1] >= three[2]) count++;
		}
		
		System.out.println(count);
	}
}