import java.util.*;
public class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int count = 0;
    int[] ary = new int[n];
    for(int c = 0;c<n;c++){
      ary[c] = sc.nextInt();
    }
    for(int c = 1;c<n-1;c++){
      if(ary[c]>ary[c-1]&&ary[c+1]>ary[c]){
        count++;
      }else if(ary[c+1]<ary[c]&&ary[c]<ary[c-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