
import java.util.Scanner;

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

        int n = scanner.nextInt();
        int[] p = new int[n];

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

        int count = 0;
        for (int i = 0 ; i < n - 2 ; i++) {
            if ((p[i] < p[i + 1] && p[i + 1] < p[i + 2])
                || (p[i + 2] < p[i + 1] && p[i + 1] < p[i])) {
                count++;
            }
        }

        System.out.println(count);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int n = scanner.nextInt();
        int[] p = new int[n];

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

        int count = 0;
        for (int i = 0 ; i < n - 2 ; i++) {
            if ((p[i] < p[i + 1] && p[i + 1] < p[i + 2])
                || (p[i + 2] < p[i + 1] && p[i + 1] < p[i])) {
                count++;
            }
        }

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

        int n = scanner.nextInt();
        int[] p = new int[n];

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

        int count = 0;
        for (int i = 0 ; i < n - 2 ; i++) {
            if ((p[i] < p[i + 1] && p[i + 1] < p[i + 2])
                || (p[i + 2] < p[i + 1] && p[i + 1] < p[i])) {
                count++;
            }
        }

        System.out.println(count);
    } main {
        Scanner scanner = new Scanner(System.in);

        int n = scanner.nextInt();
        int[] p = new int[n];

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

        int count = 0;
        for (int i = 0 ; i < n - 2 ; i++) {
            if ((p[i] < p[i + 1] && p[i + 1] < p[i + 2])
                || (p[i + 2] < p[i + 1] && p[i + 1] < p[i])) {
                count++;
            }
        }

        System.out.println(count);
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int n = scanner.nextInt(); n scanner.nextInt() scanner.nextInt scanner int[] p = new int[n]; p new int[n] n for (int i = 0 ; i < n ; i++) {
            p[i] = scanner.nextInt();
        } int i = 0 ; int i = 0 ; i 0 i < n i n i++ i++ i {
            p[i] = scanner.nextInt();
        } {
            p[i] = scanner.nextInt();
        } p[i] = scanner.nextInt() p[i] p i scanner.nextInt() scanner.nextInt scanner int count = 0; count 0 for (int i = 0 ; i < n - 2 ; i++) {
            if ((p[i] < p[i + 1] && p[i + 1] < p[i + 2])
                || (p[i + 2] < p[i + 1] && p[i + 1] < p[i])) {
                count++;
            }
        } int i = 0 ; int i = 0 ; i 0 i < n - 2 i n - 2 n 2 i++ i++ i {
            if ((p[i] < p[i + 1] && p[i + 1] < p[i + 2])
                || (p[i + 2] < p[i + 1] && p[i + 1] < p[i])) {
                count++;
            }
        } {
            if ((p[i] < p[i + 1] && p[i + 1] < p[i + 2])
                || (p[i + 2] < p[i + 1] && p[i + 1] < p[i])) {
                count++;
            }
        } if ((p[i] < p[i + 1] && p[i + 1] < p[i + 2])
                || (p[i + 2] < p[i + 1] && p[i + 1] < p[i])) {
                count++;
            } (p[i] < p[i + 1] && p[i + 1] < p[i + 2])
                || (p[i + 2] < p[i + 1] && p[i + 1] < p[i]) (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 (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 {
                count++;
            } 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 scanner = new Scanner(System.in);

        int n = scanner.nextInt();
        int[] p = new int[n];

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

        int count = 0;
        for (int i = 0 ; i < n - 2 ; i++) {
            if ((p[i] < p[i + 1] && p[i + 1] < p[i + 2])
                || (p[i + 2] < p[i + 1] && p[i + 1] < p[i])) {
                count++;
            }
        }

        System.out.println(count);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int n = scanner.nextInt();
        int[] p = new int[n];

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

        int count = 0;
        for (int i = 0 ; i < n - 2 ; i++) {
            if ((p[i] < p[i + 1] && p[i + 1] < p[i + 2])
                || (p[i + 2] < p[i + 1] && p[i + 1] < p[i])) {
                count++;
            }
        }

        System.out.println(count);
    }
} Main

import java.util.Scanner;

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

        int n = scanner.nextInt();
        int[] p = new int[n];

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

        int count = 0;
        for (int i = 0 ; i < n - 2 ; i++) {
            if ((p[i] < p[i + 1] && p[i + 1] < p[i + 2])
                || (p[i + 2] < p[i + 1] && p[i + 1] < p[i])) {
                count++;
            }
        }

        System.out.println(count);
    }
}
