import java.util.Scanner;
import java.util.InputMismatchException;

public class Main{
	public static void main(String[] args){
		Scanner scanner = new Scanner(System.in);
		String inputN = scanner.nextLine();
		
		String inputP = scanner.nextLine();
		String[] pStr = inputP.split(" ", 0);
		
		int n = Integer.parseInt(inputN);
		int pInt[] = new int[n];
		for(int i=0;i<n;i++){
			pInt[i] = Integer.parseInt(pStr[i]);
		}
		
		int iCount = 0;
		
		for(int i=0;i+2<n;i++){
			if(pInt[i] > pInt[i+1] && pInt[i+1] > pInt[i+2]){
				iCount++;
			} else if(pInt[i] < pInt[i+1] && pInt[i+1] < pInt[i+2]){
				iCount++;
			}
		}
		
		System.out.println(iCount);
	}
}
/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