import 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];

        for (int i=0; i<n; i++){
            p[i] = sc.nextInt();
        }

        int count=0;

        for (int i=0; i<n-2; i++){
            if (((p[i]<p[i+1])&(p[i+1]<p[i+2]))|((p[i]>p[i+1])&(p[i+1]>p[i+2]))){
                count++;
            }
        }

        System.out.println(count);


        }
    } import java.util.*; util.* java public class Main{

    public static void main(String args[]){

        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();
        }

        int count=0;

        for (int i=0; i<n-2; i++){
            if (((p[i]<p[i+1])&(p[i+1]<p[i+2]))|((p[i]>p[i+1])&(p[i+1]>p[i+2]))){
                count++;
            }
        }

        System.out.println(count);


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

        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();
        }

        int count=0;

        for (int i=0; i<n-2; i++){
            if (((p[i]<p[i+1])&(p[i+1]<p[i+2]))|((p[i]>p[i+1])&(p[i+1]>p[i+2]))){
                count++;
            }
        }

        System.out.println(count);


        } main {

        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();
        }

        int count=0;

        for (int i=0; i<n-2; i++){
            if (((p[i]<p[i+1])&(p[i+1]<p[i+2]))|((p[i]>p[i+1])&(p[i+1]>p[i+2]))){
                count++;
            }
        }

        System.out.println(count);


        } 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 int count=0; count 0 for (int i=0; i<n-2; i++){
            if (((p[i]<p[i+1])&(p[i+1]<p[i+2]))|((p[i]>p[i+1])&(p[i+1]>p[i+2]))){
                count++;
            }
        } 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]>p[i+1])&(p[i+1]>p[i+2]))){
                count++;
            }
        } {
            if (((p[i]<p[i+1])&(p[i+1]<p[i+2]))|((p[i]>p[i+1])&(p[i+1]>p[i+2]))){
                count++;
            }
        } if (((p[i]<p[i+1])&(p[i+1]<p[i+2]))|((p[i]>p[i+1])&(p[i+1]>p[i+2]))){
                count++;
            } ((p[i]<p[i+1])&(p[i+1]<p[i+2]))|((p[i]>p[i+1])&(p[i+1]>p[i+2])) ((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]>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 {
                count++;
            } 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 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();
        }

        int count=0;

        for (int i=0; i<n-2; i++){
            if (((p[i]<p[i+1])&(p[i+1]<p[i+2]))|((p[i]>p[i+1])&(p[i+1]>p[i+2]))){
                count++;
            }
        }

        System.out.println(count);


        }
    } public class Main{

    public static void main(String args[]){

        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();
        }

        int count=0;

        for (int i=0; i<n-2; i++){
            if (((p[i]<p[i+1])&(p[i+1]<p[i+2]))|((p[i]>p[i+1])&(p[i+1]>p[i+2]))){
                count++;
            }
        }

        System.out.println(count);


        }
    } Main
import 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];

        for (int i=0; i<n; i++){
            p[i] = sc.nextInt();
        }

        int count=0;

        for (int i=0; i<n-2; i++){
            if (((p[i]<p[i+1])&(p[i+1]<p[i+2]))|((p[i]>p[i+1])&(p[i+1]>p[i+2]))){
                count++;
            }
        }

        System.out.println(count);


        }
    }
