import java.util.Scanner;
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 total =0;
      for(int i=1; i<n-1; i++){
      if(a[i]>a[i-1] && a[i]<a[i+1]){
        total++;
      }
      else if(a[i]<a[i-1] && a[i]>a[i+1]){
        total++;
      }
      }
        System.out.println(total);
      }
}
/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