import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
	public static void main(String[] args) {
		BufferedReader buff = new BufferedReader(new InputStreamReader(System.in));

		try {
			int count = Integer.parseInt(buff.readLine());
			String[] box = buff.readLine().split(" ");
			int[] height = new int[count];
			for(int i = 0; i < count; ++i){
				height[i] = Integer.parseInt(box[i]);
			}

			int ans = 0;
			for(int i = 1; i < count-1; ++i){
				int max = 0, min = 101;
				boolean flag = false;
				for(int j = -1; j < 2; ++j){
					if(max == height[i+j] || min == height[i+j]){
						flag = true;
						break;
					}
					if(max < height[i+j]){
						max = height[i+j];
					}
					if(min > height[i+j]){
						min = height[i+j];
					}
				}
				if(flag){
					continue;
				}
				if(max != height[i-1] && min != height[i-1] || max != height[i+1] && min != height[i+1]){
					++ans;
				}
			}

			System.out.println(ans);
		} catch (NumberFormatException e) {
			e.getStackTrace();
		} catch (IOException e) {
			e.getStackTrace();
		} catch (Exception e) {
			e.getStackTrace();
		}
	}
}