import java.util.Arrays;
import java.util.Scanner;

public class Yuki116 {


    public Yuki116() {
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int[] A = new int[N];
        for (int i = 0; i < N; i++) {
            A[i] = scanner.nextInt();
        }
        int count = 0;
        for (int i = 0; i < N - 2; i++) {
            int[] B = new int[3];
            for (int j = 0; j < 3; j++) {
                B[j] = A[i + j];
            }
            Arrays.sort(B);
            if (B[0] < B[1] && B[1] < B[2]) {
                if (B[1] == A[i] || B[1] == A[i + 2]) {
                    count++;
                }
            }
        }
        System.out.println(count);
    }

    public static void main(String[] args) {
        Yuki116 hoge = new Yuki116();
    }
}