import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] p = new int[n];
    for (int i = 0; i < n; i++) {
      p[i] = Integer.parseInt(sc.next());
    }

    int cnt = 0;
    for (int i = 1; i < n - 1; i++) {
      if (Math.min(p[i - 1], p[i]) == p[i]) {
        if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        }
      } else {
        if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        }
      }
    }
    System.out.println(cnt);
  }
} import java.util.Scanner; Scanner java.util public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] p = new int[n];
    for (int i = 0; i < n; i++) {
      p[i] = Integer.parseInt(sc.next());
    }

    int cnt = 0;
    for (int i = 1; i < n - 1; i++) {
      if (Math.min(p[i - 1], p[i]) == p[i]) {
        if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        }
      } else {
        if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        }
      }
    }
    System.out.println(cnt);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] p = new int[n];
    for (int i = 0; i < n; i++) {
      p[i] = Integer.parseInt(sc.next());
    }

    int cnt = 0;
    for (int i = 1; i < n - 1; i++) {
      if (Math.min(p[i - 1], p[i]) == p[i]) {
        if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        }
      } else {
        if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        }
      }
    }
    System.out.println(cnt);
  } main {
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] p = new int[n];
    for (int i = 0; i < n; i++) {
      p[i] = Integer.parseInt(sc.next());
    }

    int cnt = 0;
    for (int i = 1; i < n - 1; i++) {
      if (Math.min(p[i - 1], p[i]) == p[i]) {
        if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        }
      } else {
        if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        }
      }
    }
    System.out.println(cnt);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = Integer.parseInt(sc.next()); n Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int[] p = new int[n]; p new int[n] n for (int i = 0; i < n; i++) {
      p[i] = Integer.parseInt(sc.next());
    } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
      p[i] = Integer.parseInt(sc.next());
    } {
      p[i] = Integer.parseInt(sc.next());
    } p[i] = Integer.parseInt(sc.next()) p[i] p i Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int cnt = 0; cnt 0 for (int i = 1; i < n - 1; i++) {
      if (Math.min(p[i - 1], p[i]) == p[i]) {
        if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        }
      } else {
        if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        }
      }
    } int i = 1; int i = 1; i 1 i < n - 1 i n - 1 n 1 i++ i++ i {
      if (Math.min(p[i - 1], p[i]) == p[i]) {
        if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        }
      } else {
        if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        }
      }
    } {
      if (Math.min(p[i - 1], p[i]) == p[i]) {
        if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        }
      } else {
        if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        }
      }
    } if (Math.min(p[i - 1], p[i]) == p[i]) {
        if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        }
      } else {
        if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        }
      } Math.min(p[i - 1], p[i]) == p[i] Math.min(p[i - 1], p[i]) Math.min Math p[i - 1] p i - 1 i 1 p[i] p i p[i] p i {
        if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        }
      } if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        } Math.min(p[i], p[i + 1]) == p[i + 1] Math.min(p[i], p[i + 1]) Math.min Math p[i] p i p[i + 1] p i + 1 i 1 p[i + 1] p i + 1 i 1 {
          cnt += 1;
        } cnt += 1 cnt 1 {
        if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        }
      } if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        } Math.min(p[i], p[i + 1]) == p[i] Math.min(p[i], p[i + 1]) Math.min Math p[i] p i p[i + 1] p i + 1 i 1 p[i] p i {
          cnt += 1;
        } cnt += 1 cnt 1 System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] p = new int[n];
    for (int i = 0; i < n; i++) {
      p[i] = Integer.parseInt(sc.next());
    }

    int cnt = 0;
    for (int i = 1; i < n - 1; i++) {
      if (Math.min(p[i - 1], p[i]) == p[i]) {
        if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        }
      } else {
        if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        }
      }
    }
    System.out.println(cnt);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] p = new int[n];
    for (int i = 0; i < n; i++) {
      p[i] = Integer.parseInt(sc.next());
    }

    int cnt = 0;
    for (int i = 1; i < n - 1; i++) {
      if (Math.min(p[i - 1], p[i]) == p[i]) {
        if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        }
      } else {
        if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        }
      }
    }
    System.out.println(cnt);
  }
} Main
import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] p = new int[n];
    for (int i = 0; i < n; i++) {
      p[i] = Integer.parseInt(sc.next());
    }

    int cnt = 0;
    for (int i = 1; i < n - 1; i++) {
      if (Math.min(p[i - 1], p[i]) == p[i]) {
        if (Math.min(p[i], p[i + 1]) == p[i + 1]) {
          cnt += 1;
        }
      } else {
        if (Math.min(p[i], p[i + 1]) == p[i]) {
          cnt += 1;
        }
      }
    }
    System.out.println(cnt);
  }
}
