import java.util.*;

public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Integer N = sc.nextInt();
        int p[] = new int[N+1];
        for(int i=1; i<=N; i++) {
            p[i] = sc.nextInt();
        }
        int cnt=0;
        for(int i=2; i<=N-1; i++) {
            if(p[i-1] < p[i] && p[i] < p[i+1]) {
                cnt++;
            } else if(p[i-1] > p[i] && p[i] > p[i+1]) {
                cnt++;
            }
        }
        System.out.println(cnt);
    }
}
/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