import java.util.Scanner;

public class Main{
	static boolean check(int x){
		if(a[x+1]>a[x] && a[x+1]>a[x+2] || a[x+1]<a[x] && a[x+1]<a[x+2]) return true;
		return false;
	}
	static int[] a;
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		a=new int[n];
		for(int i=0;i<n;i++) a[i]=sc.nextInt();
		int ans=0;
		for(int i=0;i+2<n;i++) if(a[i]!=a[i+1] && a[i+1]!=a[i+2] && a[i]!=a[i+2] && check(i)) ans++;
		System.out.println(ans);
	}
}