import java.util.*;

public class Main{
      public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            int N = sc.nextInt();
            int ans = 0;
        	int[] line = new int[N];
            for(int i = 0; i < N; i++){
              line[i] = sc.nextInt();
            }
        	for(int i = 1; i < N -1;i++){
              if( line[i-1] < line[i] && line[i] < line[i+1] || line[i+1] < line[i] && line[i] < line[i-1]){
                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