import java.util.Scanner;
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 ans = 0;

    for(int i=0; i<n; ++i)
      p[i] = sc.nextInt();

    for(int i=2; i<n; ++i) {
      if( p[i-1] < p[i-2] & p[i-1] < p[i]
         || p[i-1] > p[i-2] & p[i-1] > p[i]) {
        continue;
      }
      ++ans;
    }

    System.out.println(ans);
  }
} import java.util.Scanner; Scanner 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 ans = 0;

    for(int i=0; i<n; ++i)
      p[i] = sc.nextInt();

    for(int i=2; i<n; ++i) {
      if( p[i-1] < p[i-2] & p[i-1] < p[i]
         || p[i-1] > p[i-2] & p[i-1] > p[i]) {
        continue;
      }
      ++ans;
    }

    System.out.println(ans);
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] p = new int[n];
    int ans = 0;

    for(int i=0; i<n; ++i)
      p[i] = sc.nextInt();

    for(int i=2; i<n; ++i) {
      if( p[i-1] < p[i-2] & p[i-1] < p[i]
         || p[i-1] > p[i-2] & p[i-1] > p[i]) {
        continue;
      }
      ++ans;
    }

    System.out.println(ans);
  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] p = new int[n];
    int ans = 0;

    for(int i=0; i<n; ++i)
      p[i] = sc.nextInt();

    for(int i=2; i<n; ++i) {
      if( p[i-1] < p[i-2] & p[i-1] < p[i]
         || p[i-1] > p[i-2] & p[i-1] > p[i]) {
        continue;
      }
      ++ans;
    }

    System.out.println(ans);
  } 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 ans = 0; ans 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] p i sc.nextInt() sc.nextInt sc for(int i=2; i<n; ++i) {
      if( p[i-1] < p[i-2] & p[i-1] < p[i]
         || p[i-1] > p[i-2] & p[i-1] > p[i]) {
        continue;
      }
      ++ans;
    } int i=2; int i=2; i 2 i<n i n ++i ++i i {
      if( p[i-1] < p[i-2] & p[i-1] < p[i]
         || p[i-1] > p[i-2] & p[i-1] > p[i]) {
        continue;
      }
      ++ans;
    } {
      if( p[i-1] < p[i-2] & p[i-1] < p[i]
         || p[i-1] > p[i-2] & p[i-1] > p[i]) {
        continue;
      }
      ++ans;
    } if( p[i-1] < p[i-2] & p[i-1] < p[i]
         || p[i-1] > p[i-2] & p[i-1] > p[i]) {
        continue;
      } p[i-1] < p[i-2] & p[i-1] < p[i]
         || p[i-1] > p[i-2] & p[i-1] > p[i] p[i-1] < p[i-2] & p[i-1] < p[i] p[i-1] < p[i-2] p[i-1] p i-1 i 1 p[i-2] p i-2 i 2 p[i-1] < p[i] p[i-1] p i-1 i 1 p[i] p i p[i-1] > p[i-2] & p[i-1] > p[i] p[i-1] > p[i-2] p[i-1] p i-1 i 1 p[i-2] p i-2 i 2 p[i-1] > p[i] p[i-1] p i-1 i 1 p[i] p i {
        continue;
      } continue; ++ans ans System.out.println(ans) System.out.println System.out System System.out ans 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 ans = 0;

    for(int i=0; i<n; ++i)
      p[i] = sc.nextInt();

    for(int i=2; i<n; ++i) {
      if( p[i-1] < p[i-2] & p[i-1] < p[i]
         || p[i-1] > p[i-2] & p[i-1] > p[i]) {
        continue;
      }
      ++ans;
    }

    System.out.println(ans);
  }
} 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 ans = 0;

    for(int i=0; i<n; ++i)
      p[i] = sc.nextInt();

    for(int i=2; i<n; ++i) {
      if( p[i-1] < p[i-2] & p[i-1] < p[i]
         || p[i-1] > p[i-2] & p[i-1] > p[i]) {
        continue;
      }
      ++ans;
    }

    System.out.println(ans);
  }
} Main
import java.util.Scanner;
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 ans = 0;

    for(int i=0; i<n; ++i)
      p[i] = sc.nextInt();

    for(int i=2; i<n; ++i) {
      if( p[i-1] < p[i-2] & p[i-1] < p[i]
         || p[i-1] > p[i-2] & p[i-1] > p[i]) {
        continue;
      }
      ++ans;
    }

    System.out.println(ans);
  }
}