import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        //値を取得
        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;   //カウント用の変数
        //条件を満たすものをカウント
        for (int i = 0; i < (n-2); ++i){ //要素数がn個の配列に対し、n-2回調べる
            if (p[i] < p[i+1] && p[i+1] < p[i+2] || p[i] > p[i+1] && p[i+1] > p[i+2]){
                ++count;
            }
        }
           
        //出力
        System.out.println(count);
        
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
        //値を取得
        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;   //カウント用の変数
        //条件を満たすものをカウント
        for (int i = 0; i < (n-2); ++i){ //要素数がn個の配列に対し、n-2回調べる
            if (p[i] < p[i+1] && p[i+1] < p[i+2] || p[i] > p[i+1] && p[i+1] > p[i+2]){
                ++count;
            }
        }
           
        //出力
        System.out.println(count);
        
    }
} Main public static void main(String[] args) throws Exception {
        //値を取得
        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;   //カウント用の変数
        //条件を満たすものをカウント
        for (int i = 0; i < (n-2); ++i){ //要素数がn個の配列に対し、n-2回調べる
            if (p[i] < p[i+1] && p[i+1] < p[i+2] || p[i] > p[i+1] && p[i+1] > p[i+2]){
                ++count;
            }
        }
           
        //出力
        System.out.println(count);
        
    } main {
        //値を取得
        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;   //カウント用の変数
        //条件を満たすものをカウント
        for (int i = 0; i < (n-2); ++i){ //要素数がn個の配列に対し、n-2回調べる
            if (p[i] < p[i+1] && p[i+1] < p[i+2] || p[i] > p[i+1] && p[i+1] > p[i+2]){
                ++count;
            }
        }
           
        //出力
        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){ //要素数がn個の配列に対し、n-2回調べる
            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 { //要素数がn個の配列に対し、n-2回調べる
            if (p[i] < p[i+1] && p[i+1] < p[i+2] || p[i] > p[i+1] && p[i+1] > p[i+2]){
                ++count;
            }
        } { //要素数がn個の配列に対し、n-2回調べる
            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) throws Exception {
        //値を取得
        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;   //カウント用の変数
        //条件を満たすものをカウント
        for (int i = 0; i < (n-2); ++i){ //要素数がn個の配列に対し、n-2回調べる
            if (p[i] < p[i+1] && p[i+1] < p[i+2] || p[i] > p[i+1] && p[i+1] > p[i+2]){
                ++count;
            }
        }
           
        //出力
        System.out.println(count);
        
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        //値を取得
        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;   //カウント用の変数
        //条件を満たすものをカウント
        for (int i = 0; i < (n-2); ++i){ //要素数がn個の配列に対し、n-2回調べる
            if (p[i] < p[i+1] && p[i+1] < p[i+2] || p[i] > p[i+1] && p[i+1] > p[i+2]){
                ++count;
            }
        }
           
        //出力
        System.out.println(count);
        
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        //値を取得
        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;   //カウント用の変数
        //条件を満たすものをカウント
        for (int i = 0; i < (n-2); ++i){ //要素数がn個の配列に対し、n-2回調べる
            if (p[i] < p[i+1] && p[i+1] < p[i+2] || p[i] > p[i+1] && p[i+1] > p[i+2]){
                ++count;
            }
        }
           
        //出力
        System.out.println(count);
        
    }
}
