import java.util.Scanner;

public class P1317_1029 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scanner=new Scanner(System.in);
		int count=0,i,n=scanner.nextInt();
		int [] arr=new int[n];
		for(i=0;i<arr.length;i++)
			arr[i]=scanner.nextInt();
		for(i=1;i<arr.length-1;i++) {
			if(arr[i-1]>=arr[i] && arr[i]<arr[i+1])
				count++;
		}
		System.out.println(count);

	}

}