import java.util.Scanner;

public final class Main {
    public static void main(String[] args){
        Scanner stdIn = new Scanner(System.in);
        
        int n = stdIn.nextInt();
        int[] p = new int[n];
        for(int i=0; i<p.length; i++){
            p[i] = stdIn.nextInt();
        }
        int counter = 0;

        for(int i=1; i<p.length-1; i++){
            if((p[i-1] < p[i] && p[i] <= p[i+1]) || (p[i+1] < p[i] && p[i] <= p[i-1])){
                counter++;
            }
        }

        System.out.println(counter);
    }
}
/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