import java.util.Scanner;

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