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();
		}
		scan.close();
		int cnt=0;
		for(int i=1;i<n-1;i++) {
			if(Math.max(p[i-1], Math.max(p[i], p[i+1])) != p[i]
					&& Math.min(p[i-1], Math.min(p[i], p[i+1])) != p[i]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}
} 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();
		}
		scan.close();
		int cnt=0;
		for(int i=1;i<n-1;i++) {
			if(Math.max(p[i-1], Math.max(p[i], p[i+1])) != p[i]
					&& Math.min(p[i-1], Math.min(p[i], p[i+1])) != p[i]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}
} 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();
		}
		scan.close();
		int cnt=0;
		for(int i=1;i<n-1;i++) {
			if(Math.max(p[i-1], Math.max(p[i], p[i+1])) != p[i]
					&& Math.min(p[i-1], Math.min(p[i], p[i+1])) != p[i]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	} 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();
		}
		scan.close();
		int cnt=0;
		for(int i=1;i<n-1;i++) {
			if(Math.max(p[i-1], Math.max(p[i], p[i+1])) != p[i]
					&& Math.min(p[i-1], Math.min(p[i], p[i+1])) != p[i]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	} 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 scan.close() scan.close scan int cnt=0; cnt 0 for(int i=1;i<n-1;i++) {
			if(Math.max(p[i-1], Math.max(p[i], p[i+1])) != p[i]
					&& Math.min(p[i-1], Math.min(p[i], p[i+1])) != p[i]) {
				cnt++;
			}
		} int i=1; int i=1; i 1 i<n-1 i n-1 n 1 i++ i++ i {
			if(Math.max(p[i-1], Math.max(p[i], p[i+1])) != p[i]
					&& Math.min(p[i-1], Math.min(p[i], p[i+1])) != p[i]) {
				cnt++;
			}
		} {
			if(Math.max(p[i-1], Math.max(p[i], p[i+1])) != p[i]
					&& Math.min(p[i-1], Math.min(p[i], p[i+1])) != p[i]) {
				cnt++;
			}
		} if(Math.max(p[i-1], Math.max(p[i], p[i+1])) != p[i]
					&& Math.min(p[i-1], Math.min(p[i], p[i+1])) != p[i]) {
				cnt++;
			} Math.max(p[i-1], Math.max(p[i], p[i+1])) != p[i]
					&& Math.min(p[i-1], Math.min(p[i], p[i+1])) != p[i] Math.max(p[i-1], Math.max(p[i], p[i+1])) != p[i] Math.max(p[i-1], Math.max(p[i], p[i+1])) Math.max Math p[i-1] p i-1 i 1 Math.max(p[i], p[i+1]) Math.max Math p[i] p i p[i+1] p i+1 i 1 p[i] p i Math.min(p[i-1], Math.min(p[i], p[i+1])) != p[i] Math.min(p[i-1], Math.min(p[i], p[i+1])) Math.min Math p[i-1] p i-1 i 1 Math.min(p[i], p[i+1]) Math.min Math p[i] p i p[i+1] p i+1 i 1 p[i] p i {
				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 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();
		}
		scan.close();
		int cnt=0;
		for(int i=1;i<n-1;i++) {
			if(Math.max(p[i-1], Math.max(p[i], p[i+1])) != p[i]
					&& Math.min(p[i-1], Math.min(p[i], p[i+1])) != p[i]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}
} 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();
		}
		scan.close();
		int cnt=0;
		for(int i=1;i<n-1;i++) {
			if(Math.max(p[i-1], Math.max(p[i], p[i+1])) != p[i]
					&& Math.min(p[i-1], Math.min(p[i], p[i+1])) != p[i]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}
} 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();
		}
		scan.close();
		int cnt=0;
		for(int i=1;i<n-1;i++) {
			if(Math.max(p[i-1], Math.max(p[i], p[i+1])) != p[i]
					&& Math.min(p[i-1], Math.min(p[i], p[i+1])) != p[i]) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}
}