import java.util.Scanner;
// WA 解
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 = 1; i < N - 1; i++) {
            if (A[i - 1] < A[i] && A[i] > A[i + 1] && A[i - 1] != A[i + 1]) {
                count++;
            }
        }
        System.out.println(count);
    }

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