import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in) ;
    int n = sc.nextInt();
    int[] p = new int[n];
    int count =0;
    for (int i =0; i<n; i++) {
      p[i] = sc.nextInt();
    }
    for (int i=1; i<n-1; i++) {
      if(p[i] > Math.min(p[i-1],p[i+1]) && p[i] <= Math.max(p[i-1],p[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[] p = new int[n];
    int count =0;
    for (int i =0; i<n; i++) {
      p[i] = sc.nextInt();
    }
    for (int i=1; i<n-1; i++) {
      if(p[i] > Math.min(p[i-1],p[i+1]) && p[i] <= Math.max(p[i-1],p[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[] p = new int[n];
    int count =0;
    for (int i =0; i<n; i++) {
      p[i] = sc.nextInt();
    }
    for (int i=1; i<n-1; i++) {
      if(p[i] > Math.min(p[i-1],p[i+1]) && p[i] <= Math.max(p[i-1],p[i+1])) {
        count++;
      }
    }  
    System.out.println(count);
  } main {
    Scanner sc = new Scanner(System.in) ;
    int n = sc.nextInt();
    int[] p = new int[n];
    int count =0;
    for (int i =0; i<n; i++) {
      p[i] = sc.nextInt();
    }
    for (int i=1; i<n-1; i++) {
      if(p[i] > Math.min(p[i-1],p[i+1]) && p[i] <= Math.max(p[i-1],p[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[] p = new int[n]; p new int[n] n int count =0; count 0 for (int i =0; i<n; i++) {
      p[i] = sc.nextInt();
    } int i =0; int i =0; i 0 i<n i n i++ i++ i {
      p[i] = sc.nextInt();
    } {
      p[i] = sc.nextInt();
    } p[i] = sc.nextInt() p[i] p i sc.nextInt() sc.nextInt sc for (int i=1; i<n-1; i++) {
      if(p[i] > Math.min(p[i-1],p[i+1]) && p[i] <= Math.max(p[i-1],p[i+1])) {
        count++;
      }
    } int i=1; int i=1; i 1 i<n-1 i n-1 n 1 i++ i++ i {
      if(p[i] > Math.min(p[i-1],p[i+1]) && p[i] <= Math.max(p[i-1],p[i+1])) {
        count++;
      }
    } {
      if(p[i] > Math.min(p[i-1],p[i+1]) && p[i] <= Math.max(p[i-1],p[i+1])) {
        count++;
      }
    } if(p[i] > Math.min(p[i-1],p[i+1]) && p[i] <= Math.max(p[i-1],p[i+1])) {
        count++;
      } p[i] > Math.min(p[i-1],p[i+1]) && p[i] <= Math.max(p[i-1],p[i+1]) p[i] > Math.min(p[i-1],p[i+1]) p[i] p i Math.min(p[i-1],p[i+1]) Math.min Math p[i-1] p i-1 i 1 p[i+1] p i+1 i 1 p[i] <= Math.max(p[i-1],p[i+1]) p[i] p i Math.max(p[i-1],p[i+1]) Math.max Math p[i-1] p i-1 i 1 p[i+1] p 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[] p = new int[n];
    int count =0;
    for (int i =0; i<n; i++) {
      p[i] = sc.nextInt();
    }
    for (int i=1; i<n-1; i++) {
      if(p[i] > Math.min(p[i-1],p[i+1]) && p[i] <= Math.max(p[i-1],p[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[] p = new int[n];
    int count =0;
    for (int i =0; i<n; i++) {
      p[i] = sc.nextInt();
    }
    for (int i=1; i<n-1; i++) {
      if(p[i] > Math.min(p[i-1],p[i+1]) && p[i] <= Math.max(p[i-1],p[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[] p = new int[n];
    int count =0;
    for (int i =0; i<n; i++) {
      p[i] = sc.nextInt();
    }
    for (int i=1; i<n-1; i++) {
      if(p[i] > Math.min(p[i-1],p[i+1]) && p[i] <= Math.max(p[i-1],p[i+1])) {
        count++;
      }
    }  
    System.out.println(count);
  }
}