import java.util.*;
 
public class Main{
  public static void main(String[]args){
    Scanner sc = new Scanner(System.in);
    int N = Integer.parseInt(sc.nextLine());
    int[] num = new int[N];
    for(int i = 0; i < N; i++){
      num[i] = Integer.parseInt(sc.next());
    }
    int ans = 0;
    
    for(int i = 1; i < N-1; i++){
      if((num[i-1] <= num[i] && num[i] <= num[i+1])
        	|| (num[i-1] >= num[i] && num[i] >= num[i+1])){
        ans++;
      }
    }
    System.out.println(ans);
  }
} import java.util.*; util.* java public class Main{
  public static void main(String[]args){
    Scanner sc = new Scanner(System.in);
    int N = Integer.parseInt(sc.nextLine());
    int[] num = new int[N];
    for(int i = 0; i < N; i++){
      num[i] = Integer.parseInt(sc.next());
    }
    int ans = 0;
    
    for(int i = 1; i < N-1; i++){
      if((num[i-1] <= num[i] && num[i] <= num[i+1])
        	|| (num[i-1] >= num[i] && num[i] >= num[i+1])){
        ans++;
      }
    }
    System.out.println(ans);
  }
} Main public static void main(String[]args){
    Scanner sc = new Scanner(System.in);
    int N = Integer.parseInt(sc.nextLine());
    int[] num = new int[N];
    for(int i = 0; i < N; i++){
      num[i] = Integer.parseInt(sc.next());
    }
    int ans = 0;
    
    for(int i = 1; i < N-1; i++){
      if((num[i-1] <= num[i] && num[i] <= num[i+1])
        	|| (num[i-1] >= num[i] && num[i] >= num[i+1])){
        ans++;
      }
    }
    System.out.println(ans);
  } main {
    Scanner sc = new Scanner(System.in);
    int N = Integer.parseInt(sc.nextLine());
    int[] num = new int[N];
    for(int i = 0; i < N; i++){
      num[i] = Integer.parseInt(sc.next());
    }
    int ans = 0;
    
    for(int i = 1; i < N-1; i++){
      if((num[i-1] <= num[i] && num[i] <= num[i+1])
        	|| (num[i-1] >= num[i] && num[i] >= num[i+1])){
        ans++;
      }
    }
    System.out.println(ans);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = Integer.parseInt(sc.nextLine()); N Integer.parseInt(sc.nextLine()) Integer.parseInt Integer sc.nextLine() sc.nextLine sc int[] num = new int[N]; num new int[N] N for(int i = 0; i < N; i++){
      num[i] = Integer.parseInt(sc.next());
    } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
      num[i] = Integer.parseInt(sc.next());
    } {
      num[i] = Integer.parseInt(sc.next());
    } num[i] = Integer.parseInt(sc.next()) num[i] num i Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int ans = 0; ans 0 for(int i = 1; i < N-1; i++){
      if((num[i-1] <= num[i] && num[i] <= num[i+1])
        	|| (num[i-1] >= num[i] && num[i] >= num[i+1])){
        ans++;
      }
    } int i = 1; int i = 1; i 1 i < N-1 i N-1 N 1 i++ i++ i {
      if((num[i-1] <= num[i] && num[i] <= num[i+1])
        	|| (num[i-1] >= num[i] && num[i] >= num[i+1])){
        ans++;
      }
    } {
      if((num[i-1] <= num[i] && num[i] <= num[i+1])
        	|| (num[i-1] >= num[i] && num[i] >= num[i+1])){
        ans++;
      }
    } if((num[i-1] <= num[i] && num[i] <= num[i+1])
        	|| (num[i-1] >= num[i] && num[i] >= num[i+1])){
        ans++;
      } (num[i-1] <= num[i] && num[i] <= num[i+1])
        	|| (num[i-1] >= num[i] && num[i] >= num[i+1]) (num[i-1] <= num[i] && num[i] <= num[i+1]) num[i-1] <= num[i] num[i-1] num i-1 i 1 num[i] num i num[i] <= num[i+1] num[i] num i num[i+1] num i+1 i 1 (num[i-1] >= num[i] && num[i] >= num[i+1]) num[i-1] >= num[i] num[i-1] num i-1 i 1 num[i] num i num[i] >= num[i+1] num[i] num i num[i+1] num i+1 i 1 {
        ans++;
      } ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[]args args public class Main{
  public static void main(String[]args){
    Scanner sc = new Scanner(System.in);
    int N = Integer.parseInt(sc.nextLine());
    int[] num = new int[N];
    for(int i = 0; i < N; i++){
      num[i] = Integer.parseInt(sc.next());
    }
    int ans = 0;
    
    for(int i = 1; i < N-1; i++){
      if((num[i-1] <= num[i] && num[i] <= num[i+1])
        	|| (num[i-1] >= num[i] && num[i] >= num[i+1])){
        ans++;
      }
    }
    System.out.println(ans);
  }
} public class Main{
  public static void main(String[]args){
    Scanner sc = new Scanner(System.in);
    int N = Integer.parseInt(sc.nextLine());
    int[] num = new int[N];
    for(int i = 0; i < N; i++){
      num[i] = Integer.parseInt(sc.next());
    }
    int ans = 0;
    
    for(int i = 1; i < N-1; i++){
      if((num[i-1] <= num[i] && num[i] <= num[i+1])
        	|| (num[i-1] >= num[i] && num[i] >= num[i+1])){
        ans++;
      }
    }
    System.out.println(ans);
  }
} Main
import java.util.*;
 
public class Main{
  public static void main(String[]args){
    Scanner sc = new Scanner(System.in);
    int N = Integer.parseInt(sc.nextLine());
    int[] num = new int[N];
    for(int i = 0; i < N; i++){
      num[i] = Integer.parseInt(sc.next());
    }
    int ans = 0;
    
    for(int i = 1; i < N-1; i++){
      if((num[i-1] <= num[i] && num[i] <= num[i+1])
        	|| (num[i-1] >= num[i] && num[i] >= num[i+1])){
        ans++;
      }
    }
    System.out.println(ans);
  }
}