import java.util.*;

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 ans = 0;
        for(int i=0; i<n; i++){
		p[i] = sc.nextInt();
}
        for(int i=1; i<n-1; i++){ 
        if(p[i]>=p[i-1] && p[i]<p[i+1]){
            ans++;
        }else if(p[i]<p[i-1] && p[i]>=p[i+1]){    
            ans++;
    }
}
        System.out.print(ans);    
        }
}

/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