import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        final Scanner sc = new Scanner(System.in);

        final int n = sc.nextInt();

        final int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i < n - 1; i++) {
            if (Math.min(p[i-1], p[i+1]) < p[i] && p[i] < Math.max(p[i-1], p[i+1])) {
                ans++;
            }
        }

        System.out.println(ans);
    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        final Scanner sc = new Scanner(System.in);

        final int n = sc.nextInt();

        final int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i < n - 1; i++) {
            if (Math.min(p[i-1], p[i+1]) < p[i] && p[i] < Math.max(p[i-1], p[i+1])) {
                ans++;
            }
        }

        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        final Scanner sc = new Scanner(System.in);

        final int n = sc.nextInt();

        final int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i < n - 1; i++) {
            if (Math.min(p[i-1], p[i+1]) < p[i] && p[i] < Math.max(p[i-1], p[i+1])) {
                ans++;
            }
        }

        System.out.println(ans);
    } main {
        final Scanner sc = new Scanner(System.in);

        final int n = sc.nextInt();

        final int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i < n - 1; i++) {
            if (Math.min(p[i-1], p[i+1]) < p[i] && p[i] < Math.max(p[i-1], p[i+1])) {
                ans++;
            }
        }

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

    public static void main(String[] args) {
        final Scanner sc = new Scanner(System.in);

        final int n = sc.nextInt();

        final int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i < n - 1; i++) {
            if (Math.min(p[i-1], p[i+1]) < p[i] && p[i] < Math.max(p[i-1], p[i+1])) {
                ans++;
            }
        }

        System.out.println(ans);
    }
} public class Main {

    public static void main(String[] args) {
        final Scanner sc = new Scanner(System.in);

        final int n = sc.nextInt();

        final int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i < n - 1; i++) {
            if (Math.min(p[i-1], p[i+1]) < p[i] && p[i] < Math.max(p[i-1], p[i+1])) {
                ans++;
            }
        }

        System.out.println(ans);
    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        final Scanner sc = new Scanner(System.in);

        final int n = sc.nextInt();

        final int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i < n - 1; i++) {
            if (Math.min(p[i-1], p[i+1]) < p[i] && p[i] < Math.max(p[i-1], p[i+1])) {
                ans++;
            }
        }

        System.out.println(ans);
    }
}
