import 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[] ar = new int[n];
    for(int i=0;i<n;i++){
      ar[i] = sc.nextInt();
    }
    for(int j=1;j<n-1;j++){
      if((ar[j-1] < ar[j] && ar[j] < ar[j+1]) || (ar[j-1] > ar[j] && ar[j] > ar[j+1])){
        count++;
      }
    }
    System.out.println(count);
  }
} import java.util.*; util.* java public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int count = 0;
    int[] ar = new int[n];
    for(int i=0;i<n;i++){
      ar[i] = sc.nextInt();
    }
    for(int j=1;j<n-1;j++){
      if((ar[j-1] < ar[j] && ar[j] < ar[j+1]) || (ar[j-1] > ar[j] && ar[j] > ar[j+1])){
        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[] ar = new int[n];
    for(int i=0;i<n;i++){
      ar[i] = sc.nextInt();
    }
    for(int j=1;j<n-1;j++){
      if((ar[j-1] < ar[j] && ar[j] < ar[j+1]) || (ar[j-1] > ar[j] && ar[j] > ar[j+1])){
        count++;
      }
    }
    System.out.println(count);
  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int count = 0;
    int[] ar = new int[n];
    for(int i=0;i<n;i++){
      ar[i] = sc.nextInt();
    }
    for(int j=1;j<n-1;j++){
      if((ar[j-1] < ar[j] && ar[j] < ar[j+1]) || (ar[j-1] > ar[j] && ar[j] > ar[j+1])){
        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[] ar = new int[n]; ar new int[n] n for(int i=0;i<n;i++){
      ar[i] = sc.nextInt();
    } int i=0; int i=0; i 0 i<n i n i++ i++ i {
      ar[i] = sc.nextInt();
    } {
      ar[i] = sc.nextInt();
    } ar[i] = sc.nextInt() ar[i] ar i sc.nextInt() sc.nextInt sc for(int j=1;j<n-1;j++){
      if((ar[j-1] < ar[j] && ar[j] < ar[j+1]) || (ar[j-1] > ar[j] && ar[j] > ar[j+1])){
        count++;
      }
    } int j=1; int j=1; j 1 j<n-1 j n-1 n 1 j++ j++ j {
      if((ar[j-1] < ar[j] && ar[j] < ar[j+1]) || (ar[j-1] > ar[j] && ar[j] > ar[j+1])){
        count++;
      }
    } {
      if((ar[j-1] < ar[j] && ar[j] < ar[j+1]) || (ar[j-1] > ar[j] && ar[j] > ar[j+1])){
        count++;
      }
    } if((ar[j-1] < ar[j] && ar[j] < ar[j+1]) || (ar[j-1] > ar[j] && ar[j] > ar[j+1])){
        count++;
      } (ar[j-1] < ar[j] && ar[j] < ar[j+1]) || (ar[j-1] > ar[j] && ar[j] > ar[j+1]) (ar[j-1] < ar[j] && ar[j] < ar[j+1]) ar[j-1] < ar[j] ar[j-1] ar j-1 j 1 ar[j] ar j ar[j] < ar[j+1] ar[j] ar j ar[j+1] ar j+1 j 1 (ar[j-1] > ar[j] && ar[j] > ar[j+1]) ar[j-1] > ar[j] ar[j-1] ar j-1 j 1 ar[j] ar j ar[j] > ar[j+1] ar[j] ar j ar[j+1] ar j+1 j 1 {
        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 sc = new Scanner(System.in);
    int n = sc.nextInt();
    int count = 0;
    int[] ar = new int[n];
    for(int i=0;i<n;i++){
      ar[i] = sc.nextInt();
    }
    for(int j=1;j<n-1;j++){
      if((ar[j-1] < ar[j] && ar[j] < ar[j+1]) || (ar[j-1] > ar[j] && ar[j] > ar[j+1])){
        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[] ar = new int[n];
    for(int i=0;i<n;i++){
      ar[i] = sc.nextInt();
    }
    for(int j=1;j<n-1;j++){
      if((ar[j-1] < ar[j] && ar[j] < ar[j+1]) || (ar[j-1] > ar[j] && ar[j] > ar[j+1])){
        count++;
      }
    }
    System.out.println(count);
  }
} Main
import 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[] ar = new int[n];
    for(int i=0;i<n;i++){
      ar[i] = sc.nextInt();
    }
    for(int j=1;j<n-1;j++){
      if((ar[j-1] < ar[j] && ar[j] < ar[j+1]) || (ar[j-1] > ar[j] && ar[j] > ar[j+1])){
        count++;
      }
    }
    System.out.println(count);
  }
}