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