import java.util.*;
class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for(int i = 0; i<n; i++) {
            a[i] = sc.nextInt();
        }
        int cnt = 0;
        for(int i = 0; i<n-2; i++) {
            if(a[i]<a[i+1] && a[i+1]<=a[i+2]) cnt++;
            if(a[i+2]<a[i+1] && a[i+1]<=a[i]) cnt++;
        }
        System.out.println(cnt);
    }
}
/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