import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int ans=0;	
		int n=sc.nextInt();
		Integer P[]=new Integer[n];
		for (int i=0;i<n;i++){
		P[i]=sc.nextInt();
		}
		for (int i=1;i<n-1;i++){
			if((P[i-1]<P[i]&&P[i]<P[i+1])||(P[i+1]<P[i]&&P[i]<P[i-1])){
				ans=ans+1;
			}
		}
		
	System.out.println(ans);
	}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int ans=0;	
		int n=sc.nextInt();
		Integer P[]=new Integer[n];
		for (int i=0;i<n;i++){
		P[i]=sc.nextInt();
		}
		for (int i=1;i<n-1;i++){
			if((P[i-1]<P[i]&&P[i]<P[i+1])||(P[i+1]<P[i]&&P[i]<P[i-1])){
				ans=ans+1;
			}
		}
		
	System.out.println(ans);
	}
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int ans=0;	
		int n=sc.nextInt();
		Integer P[]=new Integer[n];
		for (int i=0;i<n;i++){
		P[i]=sc.nextInt();
		}
		for (int i=1;i<n-1;i++){
			if((P[i-1]<P[i]&&P[i]<P[i+1])||(P[i+1]<P[i]&&P[i]<P[i-1])){
				ans=ans+1;
			}
		}
		
	System.out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		int ans=0;	
		int n=sc.nextInt();
		Integer P[]=new Integer[n];
		for (int i=0;i<n;i++){
		P[i]=sc.nextInt();
		}
		for (int i=1;i<n-1;i++){
			if((P[i-1]<P[i]&&P[i]<P[i+1])||(P[i+1]<P[i]&&P[i]<P[i-1])){
				ans=ans+1;
			}
		}
		
	System.out.println(ans);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int ans=0; ans 0 int n=sc.nextInt(); n sc.nextInt() sc.nextInt sc Integer P[]=new Integer[n]; P new Integer[n] n for (int i=0;i<n;i++){
		P[i]=sc.nextInt();
		} int i=0; int i=0; i 0 i<n i n i++ i++ i {
		P[i]=sc.nextInt();
		} {
		P[i]=sc.nextInt();
		} P[i]=sc.nextInt() P[i] P i sc.nextInt() sc.nextInt sc for (int i=1;i<n-1;i++){
			if((P[i-1]<P[i]&&P[i]<P[i+1])||(P[i+1]<P[i]&&P[i]<P[i-1])){
				ans=ans+1;
			}
		} 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])||(P[i+1]<P[i]&&P[i]<P[i-1])){
				ans=ans+1;
			}
		} {
			if((P[i-1]<P[i]&&P[i]<P[i+1])||(P[i+1]<P[i]&&P[i]<P[i-1])){
				ans=ans+1;
			}
		} if((P[i-1]<P[i]&&P[i]<P[i+1])||(P[i+1]<P[i]&&P[i]<P[i-1])){
				ans=ans+1;
			} (P[i-1]<P[i]&&P[i]<P[i+1])||(P[i+1]<P[i]&&P[i]<P[i-1]) (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 (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 {
				ans=ans+1;
			} ans=ans+1 ans ans+1 ans 1 System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int ans=0;	
		int n=sc.nextInt();
		Integer P[]=new Integer[n];
		for (int i=0;i<n;i++){
		P[i]=sc.nextInt();
		}
		for (int i=1;i<n-1;i++){
			if((P[i-1]<P[i]&&P[i]<P[i+1])||(P[i+1]<P[i]&&P[i]<P[i-1])){
				ans=ans+1;
			}
		}
		
	System.out.println(ans);
	}
} public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int ans=0;	
		int n=sc.nextInt();
		Integer P[]=new Integer[n];
		for (int i=0;i<n;i++){
		P[i]=sc.nextInt();
		}
		for (int i=1;i<n-1;i++){
			if((P[i-1]<P[i]&&P[i]<P[i+1])||(P[i+1]<P[i]&&P[i]<P[i-1])){
				ans=ans+1;
			}
		}
		
	System.out.println(ans);
	}
} Main
import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int ans=0;	
		int n=sc.nextInt();
		Integer P[]=new Integer[n];
		for (int i=0;i<n;i++){
		P[i]=sc.nextInt();
		}
		for (int i=1;i<n-1;i++){
			if((P[i-1]<P[i]&&P[i]<P[i+1])||(P[i+1]<P[i]&&P[i]<P[i-1])){
				ans=ans+1;
			}
		}
		
	System.out.println(ans);
	}
}