import java.util.*;
 
public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
	    int[] number = new int[N];
	    int count = 0;

	    for(int i=0; i<N; i++){
	      number[i] = sc.nextInt();
	    }
	    for(int i=1; i<N-1; i++){
	      if((number[i-1]<=number[i])&&(number[i]<=number[i+1])){
	        count++;
	      }else if((number[i+1]<=number[i])&&(number[i]<=number[i-1])){
	        count++;
	      }
	    }
	    System.out.println(count);
	}

}
/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