import java.util.*;
import java.io.*;



public class Main{
    static int INFTY=Integer.MAX_VALUE;
    public static void main (String args[]){
        //初期処理
        Scanner sc=new Scanner(System.in);
        // BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        // try{
            // int n = Integer.parseInt(br.readLine());
            
        int n=sc.nextInt();
        int[] arr = new int[n];
        int ans=0;

        for(int i=0;i<n;i++){
            arr[i]=sc.nextInt();
        }
        for(int i=0;i<n-2;i++){
            if((arr[i]<arr[i+1]&&arr[i+1]<arr[i+2])||(arr[i+2]<arr[i+1]&&arr[i+1]<arr[i])){
             ans++;   
            }
        }
        System.out.println(ans);
    }
} import java.util.*; util.* java import java.io.*; io.* java public class Main{
    static int INFTY=Integer.MAX_VALUE;
    public static void main (String args[]){
        //初期処理
        Scanner sc=new Scanner(System.in);
        // BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        // try{
            // int n = Integer.parseInt(br.readLine());
            
        int n=sc.nextInt();
        int[] arr = new int[n];
        int ans=0;

        for(int i=0;i<n;i++){
            arr[i]=sc.nextInt();
        }
        for(int i=0;i<n-2;i++){
            if((arr[i]<arr[i+1]&&arr[i+1]<arr[i+2])||(arr[i+2]<arr[i+1]&&arr[i+1]<arr[i])){
             ans++;   
            }
        }
        System.out.println(ans);
    }
} Main static int INFTY=Integer.MAX_VALUE; INFTY Integer.MAX_VALUE Integer Integer.MAX_VALUE public static void main (String args[]){
        //初期処理
        Scanner sc=new Scanner(System.in);
        // BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        // try{
            // int n = Integer.parseInt(br.readLine());
            
        int n=sc.nextInt();
        int[] arr = new int[n];
        int ans=0;

        for(int i=0;i<n;i++){
            arr[i]=sc.nextInt();
        }
        for(int i=0;i<n-2;i++){
            if((arr[i]<arr[i+1]&&arr[i+1]<arr[i+2])||(arr[i+2]<arr[i+1]&&arr[i+1]<arr[i])){
             ans++;   
            }
        }
        System.out.println(ans);
    } main {
        //初期処理
        Scanner sc=new Scanner(System.in);
        // BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        // try{
            // int n = Integer.parseInt(br.readLine());
            
        int n=sc.nextInt();
        int[] arr = new int[n];
        int ans=0;

        for(int i=0;i<n;i++){
            arr[i]=sc.nextInt();
        }
        for(int i=0;i<n-2;i++){
            if((arr[i]<arr[i+1]&&arr[i+1]<arr[i+2])||(arr[i+2]<arr[i+1]&&arr[i+1]<arr[i])){
             ans++;   
            }
        }
        System.out.println(ans);
    } Scanner sc=new Scanner(System.in); sc new Scanner(System.in) int n=sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] arr = new int[n]; arr new int[n] n int ans=0; ans 0 for(int i=0;i<n;i++){
            arr[i]=sc.nextInt();
        } int i=0; int i=0; i 0 i<n i n i++ i++ i {
            arr[i]=sc.nextInt();
        } {
            arr[i]=sc.nextInt();
        } arr[i]=sc.nextInt() arr[i] arr i sc.nextInt() sc.nextInt sc for(int i=0;i<n-2;i++){
            if((arr[i]<arr[i+1]&&arr[i+1]<arr[i+2])||(arr[i+2]<arr[i+1]&&arr[i+1]<arr[i])){
             ans++;   
            }
        } int i=0; int i=0; i 0 i<n-2 i n-2 n 2 i++ i++ i {
            if((arr[i]<arr[i+1]&&arr[i+1]<arr[i+2])||(arr[i+2]<arr[i+1]&&arr[i+1]<arr[i])){
             ans++;   
            }
        } {
            if((arr[i]<arr[i+1]&&arr[i+1]<arr[i+2])||(arr[i+2]<arr[i+1]&&arr[i+1]<arr[i])){
             ans++;   
            }
        } if((arr[i]<arr[i+1]&&arr[i+1]<arr[i+2])||(arr[i+2]<arr[i+1]&&arr[i+1]<arr[i])){
             ans++;   
            } (arr[i]<arr[i+1]&&arr[i+1]<arr[i+2])||(arr[i+2]<arr[i+1]&&arr[i+1]<arr[i]) (arr[i]<arr[i+1]&&arr[i+1]<arr[i+2]) arr[i]<arr[i+1] arr[i] arr i arr[i+1] arr i+1 i 1 arr[i+1]<arr[i+2] arr[i+1] arr i+1 i 1 arr[i+2] arr i+2 i 2 (arr[i+2]<arr[i+1]&&arr[i+1]<arr[i]) arr[i+2]<arr[i+1] arr[i+2] arr i+2 i 2 arr[i+1] arr i+1 i 1 arr[i+1]<arr[i] arr[i+1] arr i+1 i 1 arr[i] arr i {
             ans++;   
            } ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String args[] args public class Main{
    static int INFTY=Integer.MAX_VALUE;
    public static void main (String args[]){
        //初期処理
        Scanner sc=new Scanner(System.in);
        // BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        // try{
            // int n = Integer.parseInt(br.readLine());
            
        int n=sc.nextInt();
        int[] arr = new int[n];
        int ans=0;

        for(int i=0;i<n;i++){
            arr[i]=sc.nextInt();
        }
        for(int i=0;i<n-2;i++){
            if((arr[i]<arr[i+1]&&arr[i+1]<arr[i+2])||(arr[i+2]<arr[i+1]&&arr[i+1]<arr[i])){
             ans++;   
            }
        }
        System.out.println(ans);
    }
} public class Main{
    static int INFTY=Integer.MAX_VALUE;
    public static void main (String args[]){
        //初期処理
        Scanner sc=new Scanner(System.in);
        // BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        // try{
            // int n = Integer.parseInt(br.readLine());
            
        int n=sc.nextInt();
        int[] arr = new int[n];
        int ans=0;

        for(int i=0;i<n;i++){
            arr[i]=sc.nextInt();
        }
        for(int i=0;i<n-2;i++){
            if((arr[i]<arr[i+1]&&arr[i+1]<arr[i+2])||(arr[i+2]<arr[i+1]&&arr[i+1]<arr[i])){
             ans++;   
            }
        }
        System.out.println(ans);
    }
} Main
import java.util.*;
import java.io.*;



public class Main{
    static int INFTY=Integer.MAX_VALUE;
    public static void main (String args[]){
        //初期処理
        Scanner sc=new Scanner(System.in);
        // BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        // try{
            // int n = Integer.parseInt(br.readLine());
            
        int n=sc.nextInt();
        int[] arr = new int[n];
        int ans=0;

        for(int i=0;i<n;i++){
            arr[i]=sc.nextInt();
        }
        for(int i=0;i<n-2;i++){
            if((arr[i]<arr[i+1]&&arr[i+1]<arr[i+2])||(arr[i+2]<arr[i+1]&&arr[i+1]<arr[i])){
             ans++;   
            }
        }
        System.out.println(ans);
    }
}