import java.util.Scanner;
public class Main {
    public static void main(String[] args){

    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[]p = new int[n];
    
    int cou = 0;
    for(int i=0; i<n; i++) {
    	p[i] = sc.nextInt();
    }
    for(int i=0; i<n-2; i++) {
    	if(p[i+1]<p[i] && p[i+1]>=p[i+2]) {
    			cou++;
    	}
    		if(p[i+1]>=p[i] && p[i+1]<p[i+2]) {
    	    	cou++;
    	}
    }
    		System.out.println(cou);
      }
}

/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