import java.util.Scanner;

public class Main {

    public static void main(String args[]) {

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

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

        System.out.println(result);
    }
} 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();
        Integer[] p = new Integer[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

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

        System.out.println(result);
    }
} Main public static void main(String args[]) {

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

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

        System.out.println(result);
    } main {

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

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

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

    public static void main(String args[]) {

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

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

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

    public static void main(String args[]) {

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

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

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

public class Main {

    public static void main(String args[]) {

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

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

        System.out.println(result);
    }
}
