import java.util.*;

class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int[] p = new int[n];
		for (int i=0;i<n;i++) {
			p[i] = Integer.parseInt(sc.next());
		}
		int cnt = 0;
		for (int i=1;i<n-1;i++) {
			if ((p[i-1]<=p[i] && p[i]<=p[i+1]) || (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