import java.util.*;

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

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