import java.util.*;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        int ans = 0;
        for (int i = 1; i < n-1; i++) {
            if(a[i] != Math.min(a[i-1], Math.min(a[i], a[i+1]))
                    && a[i] != Math.max(a[i-1], Math.max(a[i], a[i+1]))){
                ans++;
            }
        }
        System.out.println(ans);
        sc.close();

    }

} 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[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        int ans = 0;
        for (int i = 1; i < n-1; i++) {
            if(a[i] != Math.min(a[i-1], Math.min(a[i], a[i+1]))
                    && a[i] != Math.max(a[i-1], Math.max(a[i], a[i+1]))){
                ans++;
            }
        }
        System.out.println(ans);
        sc.close();

    }

} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        int ans = 0;
        for (int i = 1; i < n-1; i++) {
            if(a[i] != Math.min(a[i-1], Math.min(a[i], a[i+1]))
                    && a[i] != Math.max(a[i-1], Math.max(a[i], a[i+1]))){
                ans++;
            }
        }
        System.out.println(ans);
        sc.close();

    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        int ans = 0;
        for (int i = 1; i < n-1; i++) {
            if(a[i] != Math.min(a[i-1], Math.min(a[i], a[i+1]))
                    && a[i] != Math.max(a[i-1], Math.max(a[i], a[i+1]))){
                ans++;
            }
        }
        System.out.println(ans);
        sc.close();

    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] a = new int[n]; a new int[n] n for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            a[i] = sc.nextInt();
        } {
            a[i] = sc.nextInt();
        } a[i] = sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc int ans = 0; ans 0 for (int i = 1; i < n-1; i++) {
            if(a[i] != Math.min(a[i-1], Math.min(a[i], a[i+1]))
                    && a[i] != Math.max(a[i-1], Math.max(a[i], a[i+1]))){
                ans++;
            }
        } int i = 1; int i = 1; i 1 i < n-1 i n-1 n 1 i++ i++ i {
            if(a[i] != Math.min(a[i-1], Math.min(a[i], a[i+1]))
                    && a[i] != Math.max(a[i-1], Math.max(a[i], a[i+1]))){
                ans++;
            }
        } {
            if(a[i] != Math.min(a[i-1], Math.min(a[i], a[i+1]))
                    && a[i] != Math.max(a[i-1], Math.max(a[i], a[i+1]))){
                ans++;
            }
        } if(a[i] != Math.min(a[i-1], Math.min(a[i], a[i+1]))
                    && a[i] != Math.max(a[i-1], Math.max(a[i], a[i+1]))){
                ans++;
            } a[i] != Math.min(a[i-1], Math.min(a[i], a[i+1]))
                    && a[i] != Math.max(a[i-1], Math.max(a[i], a[i+1])) a[i] != Math.min(a[i-1], Math.min(a[i], a[i+1])) a[i] a i Math.min(a[i-1], Math.min(a[i], a[i+1])) Math.min Math a[i-1] a i-1 i 1 Math.min(a[i], a[i+1]) Math.min Math a[i] a i a[i+1] a i+1 i 1 a[i] != Math.max(a[i-1], Math.max(a[i], a[i+1])) a[i] a i Math.max(a[i-1], Math.max(a[i], a[i+1])) Math.max Math a[i-1] a i-1 i 1 Math.max(a[i], a[i+1]) Math.max Math a[i] a i a[i+1] a i+1 i 1 {
                ans++;
            } ans++ ans System.out.println(ans) System.out.println System.out System System.out ans sc.close() sc.close sc String[] args args public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        int ans = 0;
        for (int i = 1; i < n-1; i++) {
            if(a[i] != Math.min(a[i-1], Math.min(a[i], a[i+1]))
                    && a[i] != Math.max(a[i-1], Math.max(a[i], a[i+1]))){
                ans++;
            }
        }
        System.out.println(ans);
        sc.close();

    }

} public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        int ans = 0;
        for (int i = 1; i < n-1; i++) {
            if(a[i] != Math.min(a[i-1], Math.min(a[i], a[i+1]))
                    && a[i] != Math.max(a[i-1], Math.max(a[i], a[i+1]))){
                ans++;
            }
        }
        System.out.println(ans);
        sc.close();

    }

} Main
import java.util.*;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        int ans = 0;
        for (int i = 1; i < n-1; i++) {
            if(a[i] != Math.min(a[i-1], Math.min(a[i], a[i+1]))
                    && a[i] != Math.max(a[i-1], Math.max(a[i], a[i+1]))){
                ans++;
            }
        }
        System.out.println(ans);
        sc.close();

    }

}
