import java.util.Scanner;
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();
        }
        sc.close();
        int s = 0;
        for(int i = 0 ; i <= n - 3 ; i++ ){
            if(p[i] < p[i + 1] && p[i + 1] < p[i + 2]){
                s++;
            }else if(p[i + 2] < p[i + 1] && p[i + 1] < p[i]){
                s++;
            }
        }
        System.out.println(s);
    }
} import java.util.Scanner; Scanner 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();
        }
        sc.close();
        int s = 0;
        for(int i = 0 ; i <= n - 3 ; i++ ){
            if(p[i] < p[i + 1] && p[i + 1] < p[i + 2]){
                s++;
            }else if(p[i + 2] < p[i + 1] && p[i + 1] < p[i]){
                s++;
            }
        }
        System.out.println(s);
    }
} 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();
        }
        sc.close();
        int s = 0;
        for(int i = 0 ; i <= n - 3 ; i++ ){
            if(p[i] < p[i + 1] && p[i + 1] < p[i + 2]){
                s++;
            }else if(p[i + 2] < p[i + 1] && p[i + 1] < p[i]){
                s++;
            }
        }
        System.out.println(s);
    } 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();
        }
        sc.close();
        int s = 0;
        for(int i = 0 ; i <= n - 3 ; i++ ){
            if(p[i] < p[i + 1] && p[i + 1] < p[i + 2]){
                s++;
            }else if(p[i + 2] < p[i + 1] && p[i + 1] < p[i]){
                s++;
            }
        }
        System.out.println(s);
    } 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 sc.close() sc.close sc int s = 0; s 0 for(int i = 0 ; i <= n - 3 ; i++ ){
            if(p[i] < p[i + 1] && p[i + 1] < p[i + 2]){
                s++;
            }else if(p[i + 2] < p[i + 1] && p[i + 1] < p[i]){
                s++;
            }
        } int i = 0 ; int i = 0 ; i 0 i <= n - 3 i n - 3 n 3 i++ i++ i {
            if(p[i] < p[i + 1] && p[i + 1] < p[i + 2]){
                s++;
            }else if(p[i + 2] < p[i + 1] && p[i + 1] < p[i]){
                s++;
            }
        } {
            if(p[i] < p[i + 1] && p[i + 1] < p[i + 2]){
                s++;
            }else if(p[i + 2] < p[i + 1] && p[i + 1] < p[i]){
                s++;
            }
        } if(p[i] < p[i + 1] && p[i + 1] < p[i + 2]){
                s++;
            }else if(p[i + 2] < p[i + 1] && p[i + 1] < p[i]){
                s++;
            } 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 {
                s++;
            } s++ s if(p[i + 2] < p[i + 1] && p[i + 1] < p[i]){
                s++;
            } p[i + 2] < p[i + 1] && p[i + 1] < p[i] p[i + 2] < p[i + 1] p[i + 2] p i + 2 i 2 p[i + 1] p i + 1 i 1 p[i + 1] < p[i] p[i + 1] p i + 1 i 1 p[i] p i {
                s++;
            } s++ s System.out.println(s) System.out.println System.out System System.out s 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();
        }
        sc.close();
        int s = 0;
        for(int i = 0 ; i <= n - 3 ; i++ ){
            if(p[i] < p[i + 1] && p[i + 1] < p[i + 2]){
                s++;
            }else if(p[i + 2] < p[i + 1] && p[i + 1] < p[i]){
                s++;
            }
        }
        System.out.println(s);
    }
} 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();
        }
        sc.close();
        int s = 0;
        for(int i = 0 ; i <= n - 3 ; i++ ){
            if(p[i] < p[i + 1] && p[i + 1] < p[i + 2]){
                s++;
            }else if(p[i + 2] < p[i + 1] && p[i + 1] < p[i]){
                s++;
            }
        }
        System.out.println(s);
    }
} Main
import java.util.Scanner;
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();
        }
        sc.close();
        int s = 0;
        for(int i = 0 ; i <= n - 3 ; i++ ){
            if(p[i] < p[i + 1] && p[i + 1] < p[i + 2]){
                s++;
            }else if(p[i + 2] < p[i + 1] && p[i + 1] < p[i]){
                s++;
            }
        }
        System.out.println(s);
    }
}