import java.util.*;

public class Main {
  public static void main(String[] args ) throws Exception {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int Nums[]=new int[N];
    int count=0;
    for(int i=0;i<N;i++){
      Nums[i]=sc.nextInt();
    }
  for(int i=2;i<N;i++){
    if(Nums[i-2]<Nums[i-1]&&Nums[i-1]<Nums[i]){
      count++;
   	 }else if(Nums[i-2]>Nums[i-1]&&Nums[i-1]>Nums[i]){
      count++;
    }
  	}System.out.println(count);
  }
}
 import java.util.*; util.* java public class Main {
  public static void main(String[] args ) throws Exception {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int Nums[]=new int[N];
    int count=0;
    for(int i=0;i<N;i++){
      Nums[i]=sc.nextInt();
    }
  for(int i=2;i<N;i++){
    if(Nums[i-2]<Nums[i-1]&&Nums[i-1]<Nums[i]){
      count++;
   	 }else if(Nums[i-2]>Nums[i-1]&&Nums[i-1]>Nums[i]){
      count++;
    }
  	}System.out.println(count);
  }
} Main public static void main(String[] args ) throws Exception {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int Nums[]=new int[N];
    int count=0;
    for(int i=0;i<N;i++){
      Nums[i]=sc.nextInt();
    }
  for(int i=2;i<N;i++){
    if(Nums[i-2]<Nums[i-1]&&Nums[i-1]<Nums[i]){
      count++;
   	 }else if(Nums[i-2]>Nums[i-1]&&Nums[i-1]>Nums[i]){
      count++;
    }
  	}System.out.println(count);
  } main {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int Nums[]=new int[N];
    int count=0;
    for(int i=0;i<N;i++){
      Nums[i]=sc.nextInt();
    }
  for(int i=2;i<N;i++){
    if(Nums[i-2]<Nums[i-1]&&Nums[i-1]<Nums[i]){
      count++;
   	 }else if(Nums[i-2]>Nums[i-1]&&Nums[i-1]>Nums[i]){
      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 Nums[]=new int[N]; Nums new int[N] N int count=0; count 0 for(int i=0;i<N;i++){
      Nums[i]=sc.nextInt();
    } int i=0; int i=0; i 0 i<N i N 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=2;i<N;i++){
    if(Nums[i-2]<Nums[i-1]&&Nums[i-1]<Nums[i]){
      count++;
   	 }else if(Nums[i-2]>Nums[i-1]&&Nums[i-1]>Nums[i]){
      count++;
    }
  	} int i=2; int i=2; i 2 i<N i N i++ i++ i {
    if(Nums[i-2]<Nums[i-1]&&Nums[i-1]<Nums[i]){
      count++;
   	 }else if(Nums[i-2]>Nums[i-1]&&Nums[i-1]>Nums[i]){
      count++;
    }
  	} {
    if(Nums[i-2]<Nums[i-1]&&Nums[i-1]<Nums[i]){
      count++;
   	 }else if(Nums[i-2]>Nums[i-1]&&Nums[i-1]>Nums[i]){
      count++;
    }
  	} if(Nums[i-2]<Nums[i-1]&&Nums[i-1]<Nums[i]){
      count++;
   	 }else if(Nums[i-2]>Nums[i-1]&&Nums[i-1]>Nums[i]){
      count++;
    } Nums[i-2]<Nums[i-1]&&Nums[i-1]<Nums[i] Nums[i-2]<Nums[i-1] Nums[i-2] Nums i-2 i 2 Nums[i-1] Nums i-1 i 1 Nums[i-1]<Nums[i] Nums[i-1] Nums i-1 i 1 Nums[i] Nums i {
      count++;
   	 } count++ count if(Nums[i-2]>Nums[i-1]&&Nums[i-1]>Nums[i]){
      count++;
    } Nums[i-2]>Nums[i-1]&&Nums[i-1]>Nums[i] Nums[i-2]>Nums[i-1] Nums[i-2] Nums i-2 i 2 Nums[i-1] Nums i-1 i 1 Nums[i-1]>Nums[i] Nums[i-1] Nums i-1 i 1 Nums[i] Nums i {
      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 ) throws Exception {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int Nums[]=new int[N];
    int count=0;
    for(int i=0;i<N;i++){
      Nums[i]=sc.nextInt();
    }
  for(int i=2;i<N;i++){
    if(Nums[i-2]<Nums[i-1]&&Nums[i-1]<Nums[i]){
      count++;
   	 }else if(Nums[i-2]>Nums[i-1]&&Nums[i-1]>Nums[i]){
      count++;
    }
  	}System.out.println(count);
  }
} public class Main {
  public static void main(String[] args ) throws Exception {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int Nums[]=new int[N];
    int count=0;
    for(int i=0;i<N;i++){
      Nums[i]=sc.nextInt();
    }
  for(int i=2;i<N;i++){
    if(Nums[i-2]<Nums[i-1]&&Nums[i-1]<Nums[i]){
      count++;
   	 }else if(Nums[i-2]>Nums[i-1]&&Nums[i-1]>Nums[i]){
      count++;
    }
  	}System.out.println(count);
  }
} Main
import java.util.*;

public class Main {
  public static void main(String[] args ) throws Exception {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int Nums[]=new int[N];
    int count=0;
    for(int i=0;i<N;i++){
      Nums[i]=sc.nextInt();
    }
  for(int i=2;i<N;i++){
    if(Nums[i-2]<Nums[i-1]&&Nums[i-1]<Nums[i]){
      count++;
   	 }else if(Nums[i-2]>Nums[i-1]&&Nums[i-1]>Nums[i]){
      count++;
    }
  	}System.out.println(count);
  }
}

