import java.util.*;
 
public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
	    int[] number = new int[N];
	    int count = 0;

	    for(int i=0; i<N; i++){
	      number[i] = sc.nextInt();
	    }
	    for(int i=1; i<N-1; i++){
	      if((number[i-1]<=number[i])&&(number[i]<=number[i+1])){
	        count++;
	      }else if((number[i+1]<=number[i])&&(number[i]<=number[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 N = sc.nextInt();
	    int[] number = new int[N];
	    int count = 0;

	    for(int i=0; i<N; i++){
	      number[i] = sc.nextInt();
	    }
	    for(int i=1; i<N-1; i++){
	      if((number[i-1]<=number[i])&&(number[i]<=number[i+1])){
	        count++;
	      }else if((number[i+1]<=number[i])&&(number[i]<=number[i-1])){
	        count++;
	      }
	    }
	    System.out.println(count);
	}

} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
	    int[] number = new int[N];
	    int count = 0;

	    for(int i=0; i<N; i++){
	      number[i] = sc.nextInt();
	    }
	    for(int i=1; i<N-1; i++){
	      if((number[i-1]<=number[i])&&(number[i]<=number[i+1])){
	        count++;
	      }else if((number[i+1]<=number[i])&&(number[i]<=number[i-1])){
	        count++;
	      }
	    }
	    System.out.println(count);
	} main {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
	    int[] number = new int[N];
	    int count = 0;

	    for(int i=0; i<N; i++){
	      number[i] = sc.nextInt();
	    }
	    for(int i=1; i<N-1; i++){
	      if((number[i-1]<=number[i])&&(number[i]<=number[i+1])){
	        count++;
	      }else if((number[i+1]<=number[i])&&(number[i]<=number[i-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[] number = new int[N]; number new int[N] N int count = 0; count 0 for(int i=0; i<N; i++){
	      number[i] = sc.nextInt();
	    } int i=0; int i=0; i 0 i<N i N i++ i++ i {
	      number[i] = sc.nextInt();
	    } {
	      number[i] = sc.nextInt();
	    } number[i] = sc.nextInt() number[i] number i sc.nextInt() sc.nextInt sc for(int i=1; i<N-1; i++){
	      if((number[i-1]<=number[i])&&(number[i]<=number[i+1])){
	        count++;
	      }else if((number[i+1]<=number[i])&&(number[i]<=number[i-1])){
	        count++;
	      }
	    } int i=1; int i=1; i 1 i<N-1 i N-1 N 1 i++ i++ i {
	      if((number[i-1]<=number[i])&&(number[i]<=number[i+1])){
	        count++;
	      }else if((number[i+1]<=number[i])&&(number[i]<=number[i-1])){
	        count++;
	      }
	    } {
	      if((number[i-1]<=number[i])&&(number[i]<=number[i+1])){
	        count++;
	      }else if((number[i+1]<=number[i])&&(number[i]<=number[i-1])){
	        count++;
	      }
	    } if((number[i-1]<=number[i])&&(number[i]<=number[i+1])){
	        count++;
	      }else if((number[i+1]<=number[i])&&(number[i]<=number[i-1])){
	        count++;
	      } (number[i-1]<=number[i])&&(number[i]<=number[i+1]) (number[i-1]<=number[i]) number[i-1] number i-1 i 1 number[i] number i (number[i]<=number[i+1]) number[i] number i number[i+1] number i+1 i 1 {
	        count++;
	      } count++ count if((number[i+1]<=number[i])&&(number[i]<=number[i-1])){
	        count++;
	      } (number[i+1]<=number[i])&&(number[i]<=number[i-1]) (number[i+1]<=number[i]) number[i+1] number i+1 i 1 number[i] number i (number[i]<=number[i-1]) number[i] number i number[i-1] number 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 N = sc.nextInt();
	    int[] number = new int[N];
	    int count = 0;

	    for(int i=0; i<N; i++){
	      number[i] = sc.nextInt();
	    }
	    for(int i=1; i<N-1; i++){
	      if((number[i-1]<=number[i])&&(number[i]<=number[i+1])){
	        count++;
	      }else if((number[i+1]<=number[i])&&(number[i]<=number[i-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[] number = new int[N];
	    int count = 0;

	    for(int i=0; i<N; i++){
	      number[i] = sc.nextInt();
	    }
	    for(int i=1; i<N-1; i++){
	      if((number[i-1]<=number[i])&&(number[i]<=number[i+1])){
	        count++;
	      }else if((number[i+1]<=number[i])&&(number[i]<=number[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 N = sc.nextInt();
	    int[] number = new int[N];
	    int count = 0;

	    for(int i=0; i<N; i++){
	      number[i] = sc.nextInt();
	    }
	    for(int i=1; i<N-1; i++){
	      if((number[i-1]<=number[i])&&(number[i]<=number[i+1])){
	        count++;
	      }else if((number[i+1]<=number[i])&&(number[i]<=number[i-1])){
	        count++;
	      }
	    }
	    System.out.println(count);
	}

}