import java.util.List;
import java.util.ArrayList;
import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    List<Integer> list = new ArrayList<Integer>();
    int n = sc.nextInt();
    for (int i = 0; i < n; i++)
	  list.add(sc.nextInt());
    int count = 0;
    for (int i = 1; i < n - 1; i++)
      if ((list.get(i-1) > list.get(i) && list.get(i) > list.get(i+1)) || list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1))
        count++;
    System.out.print(count);
  }
} import java.util.List; List java.util import java.util.ArrayList; ArrayList java.util import java.util.Scanner; Scanner java.util public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    List<Integer> list = new ArrayList<Integer>();
    int n = sc.nextInt();
    for (int i = 0; i < n; i++)
	  list.add(sc.nextInt());
    int count = 0;
    for (int i = 1; i < n - 1; i++)
      if ((list.get(i-1) > list.get(i) && list.get(i) > list.get(i+1)) || list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1))
        count++;
    System.out.print(count);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    List<Integer> list = new ArrayList<Integer>();
    int n = sc.nextInt();
    for (int i = 0; i < n; i++)
	  list.add(sc.nextInt());
    int count = 0;
    for (int i = 1; i < n - 1; i++)
      if ((list.get(i-1) > list.get(i) && list.get(i) > list.get(i+1)) || list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1))
        count++;
    System.out.print(count);
  } main {
    Scanner sc = new Scanner(System.in);
    List<Integer> list = new ArrayList<Integer>();
    int n = sc.nextInt();
    for (int i = 0; i < n; i++)
	  list.add(sc.nextInt());
    int count = 0;
    for (int i = 1; i < n - 1; i++)
      if ((list.get(i-1) > list.get(i) && list.get(i) > list.get(i+1)) || list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1))
        count++;
    System.out.print(count);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) List<Integer> list = new ArrayList<Integer>(); list new ArrayList<Integer>() int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc for (int i = 0; i < n; i++)
	  list.add(sc.nextInt()); int i = 0; int i = 0; i 0 i < n i n i++ i++ i list.add(sc.nextInt()); list.add(sc.nextInt()) list.add list sc.nextInt() sc.nextInt sc int count = 0; count 0 for (int i = 1; i < n - 1; i++)
      if ((list.get(i-1) > list.get(i) && list.get(i) > list.get(i+1)) || list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1))
        count++; int i = 1; int i = 1; i 1 i < n - 1 i n - 1 n 1 i++ i++ i if ((list.get(i-1) > list.get(i) && list.get(i) > list.get(i+1)) || list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1))
        count++; if ((list.get(i-1) > list.get(i) && list.get(i) > list.get(i+1)) || list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1))
        count++; (list.get(i-1) > list.get(i) && list.get(i) > list.get(i+1)) || list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1) (list.get(i-1) > list.get(i) && list.get(i) > list.get(i+1)) list.get(i-1) > list.get(i) list.get(i-1) list.get list i-1 i 1 list.get(i) list.get list i list.get(i) > list.get(i+1) list.get(i) list.get list i list.get(i+1) list.get list i+1 i 1 list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1) list.get(i-1) < list.get(i) list.get(i-1) list.get list i-1 i 1 list.get(i) list.get list i list.get(i) < list.get(i+1) list.get(i) list.get list i list.get(i+1) list.get list i+1 i 1 count++ count System.out.print(count) System.out.print System.out System System.out count String[] args args public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    List<Integer> list = new ArrayList<Integer>();
    int n = sc.nextInt();
    for (int i = 0; i < n; i++)
	  list.add(sc.nextInt());
    int count = 0;
    for (int i = 1; i < n - 1; i++)
      if ((list.get(i-1) > list.get(i) && list.get(i) > list.get(i+1)) || list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1))
        count++;
    System.out.print(count);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    List<Integer> list = new ArrayList<Integer>();
    int n = sc.nextInt();
    for (int i = 0; i < n; i++)
	  list.add(sc.nextInt());
    int count = 0;
    for (int i = 1; i < n - 1; i++)
      if ((list.get(i-1) > list.get(i) && list.get(i) > list.get(i+1)) || list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1))
        count++;
    System.out.print(count);
  }
} Main
import java.util.List;
import java.util.ArrayList;
import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    List<Integer> list = new ArrayList<Integer>();
    int n = sc.nextInt();
    for (int i = 0; i < n; i++)
	  list.add(sc.nextInt());
    int count = 0;
    for (int i = 1; i < n - 1; i++)
      if ((list.get(i-1) > list.get(i) && list.get(i) > list.get(i+1)) || list.get(i-1) < list.get(i) && list.get(i) < list.get(i+1))
        count++;
    System.out.print(count);
  }
}