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);
  }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz