
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        // write your code here
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int[] p=new int[n];
        for(int i=0;i<n;i++){
            p[i]=sc.nextInt();
        }

        List<Integer> lst =new ArrayList<>();

        for(int i=0;i<n-2;i++){
            if(p[i]<=p[i+1]&&p[i+1]<=p[i+2]){
                lst.add(p[i+1]);
            }else if(p[i]>=p[i+1]&&p[i+1]>=p[i+2]){
                lst.add(p[i+1]);
            }

        }

            System.out.println(lst.size());



    }
}
 import java.util.ArrayList; ArrayList java.util import java.util.List; List java.util import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        // write your code here
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int[] p=new int[n];
        for(int i=0;i<n;i++){
            p[i]=sc.nextInt();
        }

        List<Integer> lst =new ArrayList<>();

        for(int i=0;i<n-2;i++){
            if(p[i]<=p[i+1]&&p[i+1]<=p[i+2]){
                lst.add(p[i+1]);
            }else if(p[i]>=p[i+1]&&p[i+1]>=p[i+2]){
                lst.add(p[i+1]);
            }

        }

            System.out.println(lst.size());



    }
} Main public static void main(String[] args) {
        // write your code here
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int[] p=new int[n];
        for(int i=0;i<n;i++){
            p[i]=sc.nextInt();
        }

        List<Integer> lst =new ArrayList<>();

        for(int i=0;i<n-2;i++){
            if(p[i]<=p[i+1]&&p[i+1]<=p[i+2]){
                lst.add(p[i+1]);
            }else if(p[i]>=p[i+1]&&p[i+1]>=p[i+2]){
                lst.add(p[i+1]);
            }

        }

            System.out.println(lst.size());



    } main {
        // write your code here
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int[] p=new int[n];
        for(int i=0;i<n;i++){
            p[i]=sc.nextInt();
        }

        List<Integer> lst =new ArrayList<>();

        for(int i=0;i<n-2;i++){
            if(p[i]<=p[i+1]&&p[i+1]<=p[i+2]){
                lst.add(p[i+1]);
            }else if(p[i]>=p[i+1]&&p[i+1]>=p[i+2]){
                lst.add(p[i+1]);
            }

        }

            System.out.println(lst.size());



    } 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 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 List<Integer> lst =new ArrayList<>(); lst new ArrayList<>() for(int i=0;i<n-2;i++){
            if(p[i]<=p[i+1]&&p[i+1]<=p[i+2]){
                lst.add(p[i+1]);
            }else if(p[i]>=p[i+1]&&p[i+1]>=p[i+2]){
                lst.add(p[i+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]){
                lst.add(p[i+1]);
            }else if(p[i]>=p[i+1]&&p[i+1]>=p[i+2]){
                lst.add(p[i+1]);
            }

        } {
            if(p[i]<=p[i+1]&&p[i+1]<=p[i+2]){
                lst.add(p[i+1]);
            }else if(p[i]>=p[i+1]&&p[i+1]>=p[i+2]){
                lst.add(p[i+1]);
            }

        } if(p[i]<=p[i+1]&&p[i+1]<=p[i+2]){
                lst.add(p[i+1]);
            }else if(p[i]>=p[i+1]&&p[i+1]>=p[i+2]){
                lst.add(p[i+1]);
            } 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 {
                lst.add(p[i+1]);
            } lst.add(p[i+1]) lst.add lst p[i+1] p i+1 i 1 if(p[i]>=p[i+1]&&p[i+1]>=p[i+2]){
                lst.add(p[i+1]);
            } 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 {
                lst.add(p[i+1]);
            } lst.add(p[i+1]) lst.add lst p[i+1] p i+1 i 1 System.out.println(lst.size()) System.out.println System.out System System.out lst.size() lst.size lst String[] args args public class Main {

    public static void main(String[] args) {
        // write your code here
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int[] p=new int[n];
        for(int i=0;i<n;i++){
            p[i]=sc.nextInt();
        }

        List<Integer> lst =new ArrayList<>();

        for(int i=0;i<n-2;i++){
            if(p[i]<=p[i+1]&&p[i+1]<=p[i+2]){
                lst.add(p[i+1]);
            }else if(p[i]>=p[i+1]&&p[i+1]>=p[i+2]){
                lst.add(p[i+1]);
            }

        }

            System.out.println(lst.size());



    }
} public class Main {

    public static void main(String[] args) {
        // write your code here
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int[] p=new int[n];
        for(int i=0;i<n;i++){
            p[i]=sc.nextInt();
        }

        List<Integer> lst =new ArrayList<>();

        for(int i=0;i<n-2;i++){
            if(p[i]<=p[i+1]&&p[i+1]<=p[i+2]){
                lst.add(p[i+1]);
            }else if(p[i]>=p[i+1]&&p[i+1]>=p[i+2]){
                lst.add(p[i+1]);
            }

        }

            System.out.println(lst.size());



    }
} Main

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        // write your code here
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int[] p=new int[n];
        for(int i=0;i<n;i++){
            p[i]=sc.nextInt();
        }

        List<Integer> lst =new ArrayList<>();

        for(int i=0;i<n-2;i++){
            if(p[i]<=p[i+1]&&p[i+1]<=p[i+2]){
                lst.add(p[i+1]);
            }else if(p[i]>=p[i+1]&&p[i+1]>=p[i+2]){
                lst.add(p[i+1]);
            }

        }

            System.out.println(lst.size());



    }
}

