import java.util.Scanner;

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

        int n = sc.nextInt();
        int count = 0;
        int[] p = new int[n];
        for (int i = 0; i < p.length; i++)
            p[i] = sc.nextInt();
        for (int i = 0; i <= n - 3; i++) {
            int max = p[i];
            if (max < p[i + 1])
                max = p[i + 1];
            if (max < p[i + 2])
                max = p[i + 2];
            int min = p[i];
            if (min > p[i + 1])
                min = p[i + 1];
            if (min > p[i + 2])
                min = p[i + 2];
            if (p[i + 1] == (p[i] + p[i + 1] + p[i + 2] - max - min))
                count++;
        }
        System.out.println(count);
    }
} 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 count = 0;
        int[] p = new int[n];
        for (int i = 0; i < p.length; i++)
            p[i] = sc.nextInt();
        for (int i = 0; i <= n - 3; i++) {
            int max = p[i];
            if (max < p[i + 1])
                max = p[i + 1];
            if (max < p[i + 2])
                max = p[i + 2];
            int min = p[i];
            if (min > p[i + 1])
                min = p[i + 1];
            if (min > p[i + 2])
                min = p[i + 2];
            if (p[i + 1] == (p[i] + p[i + 1] + p[i + 2] - max - min))
                count++;
        }
        System.out.println(count);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int count = 0;
        int[] p = new int[n];
        for (int i = 0; i < p.length; i++)
            p[i] = sc.nextInt();
        for (int i = 0; i <= n - 3; i++) {
            int max = p[i];
            if (max < p[i + 1])
                max = p[i + 1];
            if (max < p[i + 2])
                max = p[i + 2];
            int min = p[i];
            if (min > p[i + 1])
                min = p[i + 1];
            if (min > p[i + 2])
                min = p[i + 2];
            if (p[i + 1] == (p[i] + p[i + 1] + p[i + 2] - max - min))
                count++;
        }
        System.out.println(count);
    } main {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int count = 0;
        int[] p = new int[n];
        for (int i = 0; i < p.length; i++)
            p[i] = sc.nextInt();
        for (int i = 0; i <= n - 3; i++) {
            int max = p[i];
            if (max < p[i + 1])
                max = p[i + 1];
            if (max < p[i + 2])
                max = p[i + 2];
            int min = p[i];
            if (min > p[i + 1])
                min = p[i + 1];
            if (min > p[i + 2])
                min = p[i + 2];
            if (p[i + 1] == (p[i] + p[i + 1] + p[i + 2] - max - min))
                count++;
        }
        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 count = 0; count 0 int[] p = new int[n]; p new int[n] n for (int i = 0; i < p.length; i++)
            p[i] = sc.nextInt(); int i = 0; int i = 0; i 0 i < p.length i p.length p p.length i++ i++ i p[i] = sc.nextInt(); p[i] = sc.nextInt() p[i] p i sc.nextInt() sc.nextInt sc for (int i = 0; i <= n - 3; i++) {
            int max = p[i];
            if (max < p[i + 1])
                max = p[i + 1];
            if (max < p[i + 2])
                max = p[i + 2];
            int min = p[i];
            if (min > p[i + 1])
                min = p[i + 1];
            if (min > p[i + 2])
                min = p[i + 2];
            if (p[i + 1] == (p[i] + p[i + 1] + p[i + 2] - max - min))
                count++;
        } int i = 0; int i = 0; i 0 i <= n - 3 i n - 3 n 3 i++ i++ i {
            int max = p[i];
            if (max < p[i + 1])
                max = p[i + 1];
            if (max < p[i + 2])
                max = p[i + 2];
            int min = p[i];
            if (min > p[i + 1])
                min = p[i + 1];
            if (min > p[i + 2])
                min = p[i + 2];
            if (p[i + 1] == (p[i] + p[i + 1] + p[i + 2] - max - min))
                count++;
        } {
            int max = p[i];
            if (max < p[i + 1])
                max = p[i + 1];
            if (max < p[i + 2])
                max = p[i + 2];
            int min = p[i];
            if (min > p[i + 1])
                min = p[i + 1];
            if (min > p[i + 2])
                min = p[i + 2];
            if (p[i + 1] == (p[i] + p[i + 1] + p[i + 2] - max - min))
                count++;
        } int max = p[i]; max p[i] p i if (max < p[i + 1])
                max = p[i + 1]; max < p[i + 1] max p[i + 1] p i + 1 i 1 max = p[i + 1] max p[i + 1] p i + 1 i 1 if (max < p[i + 2])
                max = p[i + 2]; max < p[i + 2] max p[i + 2] p i + 2 i 2 max = p[i + 2] max p[i + 2] p i + 2 i 2 int min = p[i]; min p[i] p i if (min > p[i + 1])
                min = p[i + 1]; min > p[i + 1] min p[i + 1] p i + 1 i 1 min = p[i + 1] min p[i + 1] p i + 1 i 1 if (min > p[i + 2])
                min = p[i + 2]; min > p[i + 2] min p[i + 2] p i + 2 i 2 min = p[i + 2] min p[i + 2] p i + 2 i 2 if (p[i + 1] == (p[i] + p[i + 1] + p[i + 2] - max - min))
                count++; p[i + 1] == (p[i] + p[i + 1] + p[i + 2] - max - min) p[i + 1] p i + 1 i 1 (p[i] + p[i + 1] + p[i + 2] - max - min) p[i] + p[i + 1] + p[i + 2] - max - min p[i] + p[i + 1] + p[i + 2] p[i] + p[i + 1] + p[i + 2] p[i] p i p[i + 1] p i + 1 i 1 p[i + 2] p i + 2 i 2 max min 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) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int count = 0;
        int[] p = new int[n];
        for (int i = 0; i < p.length; i++)
            p[i] = sc.nextInt();
        for (int i = 0; i <= n - 3; i++) {
            int max = p[i];
            if (max < p[i + 1])
                max = p[i + 1];
            if (max < p[i + 2])
                max = p[i + 2];
            int min = p[i];
            if (min > p[i + 1])
                min = p[i + 1];
            if (min > p[i + 2])
                min = p[i + 2];
            if (p[i + 1] == (p[i] + p[i + 1] + p[i + 2] - max - min))
                count++;
        }
        System.out.println(count);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int count = 0;
        int[] p = new int[n];
        for (int i = 0; i < p.length; i++)
            p[i] = sc.nextInt();
        for (int i = 0; i <= n - 3; i++) {
            int max = p[i];
            if (max < p[i + 1])
                max = p[i + 1];
            if (max < p[i + 2])
                max = p[i + 2];
            int min = p[i];
            if (min > p[i + 1])
                min = p[i + 1];
            if (min > p[i + 2])
                min = p[i + 2];
            if (p[i + 1] == (p[i] + p[i + 1] + p[i + 2] - max - min))
                count++;
        }
        System.out.println(count);
    }
} 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 count = 0;
        int[] p = new int[n];
        for (int i = 0; i < p.length; i++)
            p[i] = sc.nextInt();
        for (int i = 0; i <= n - 3; i++) {
            int max = p[i];
            if (max < p[i + 1])
                max = p[i + 1];
            if (max < p[i + 2])
                max = p[i + 2];
            int min = p[i];
            if (min > p[i + 1])
                min = p[i + 1];
            if (min > p[i + 2])
                min = p[i + 2];
            if (p[i + 1] == (p[i] + p[i + 1] + p[i + 2] - max - min))
                count++;
        }
        System.out.println(count);
    }
}
