import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int[] a = new int[N];
    for(int i = 0; i < N; i++) {
      a[i] = sc.nextInt();
    }
    int ans = 0;
    for(int i = 0; i < N - 2; i++) {
      if(a[i] != a[i + 1] && a[i] != a[i + 2] && a[i + 1] != a[i + 2]) {
        int max = Math.max(a[i], Math.max(a[i + 1], a[i + 2]));
        int min = Math.min(a[i], Math.min(a[i + 1], a[i + 2]));
        if(a[i + 1] == max || a[i + 1] == min) ans++;
      }
    }
    System.out.println(ans);
  }
}