import java.awt.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;
import java.util.List;

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

    }

}
 import java.awt.*; awt.* java import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.*; util.* java import java.util.List; List java.util public class Main {
    public static void main(String args[]) throws IOException {
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int arr[]=new int[n];
        for (int i=0;i<n;i++){
            arr[i]=sc.nextInt();
        }
        int cnt=0;
        for (int i=1;i<n-1;i++){
            if ((arr[i]>arr[i-1] && arr[i]<arr[i+1]) || (arr[i]<arr[i-1] && arr[i]>arr[i+1]) ){
                cnt++;
            }
        }
        System.out.println(cnt);

    }

} Main public static void main(String args[]) throws IOException {
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int arr[]=new int[n];
        for (int i=0;i<n;i++){
            arr[i]=sc.nextInt();
        }
        int cnt=0;
        for (int i=1;i<n-1;i++){
            if ((arr[i]>arr[i-1] && arr[i]<arr[i+1]) || (arr[i]<arr[i-1] && arr[i]>arr[i+1]) ){
                cnt++;
            }
        }
        System.out.println(cnt);

    } main {
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int arr[]=new int[n];
        for (int i=0;i<n;i++){
            arr[i]=sc.nextInt();
        }
        int cnt=0;
        for (int i=1;i<n-1;i++){
            if ((arr[i]>arr[i-1] && arr[i]<arr[i+1]) || (arr[i]<arr[i-1] && arr[i]>arr[i+1]) ){
                cnt++;
            }
        }
        System.out.println(cnt);

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

    }

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

    }

} Main
import java.awt.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;
import java.util.List;

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

    }

}

