
import java.util.Scanner;

public class Main {

	public static void main(String[] args){
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();
		int[] p = new int[n];
		int ans = 0;

		for(int i = 0; i < n; i++)
			p[i] = in.nextInt();

		for(int i = 1; i<n-1; i++) {
			boolean dontMax = (p[i] < Math.max(p[i-1], p[i+1]));
			boolean dontMin = (p[i] > Math.min(p[i-1], p[i+1]));
			if(dontMax && dontMin)
				ans++;

		}

		System.out.println(ans);
	}

} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args){
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();
		int[] p = new int[n];
		int ans = 0;

		for(int i = 0; i < n; i++)
			p[i] = in.nextInt();

		for(int i = 1; i<n-1; i++) {
			boolean dontMax = (p[i] < Math.max(p[i-1], p[i+1]));
			boolean dontMin = (p[i] > Math.min(p[i-1], p[i+1]));
			if(dontMax && dontMin)
				ans++;

		}

		System.out.println(ans);
	}

} Main public static void main(String[] args){
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();
		int[] p = new int[n];
		int ans = 0;

		for(int i = 0; i < n; i++)
			p[i] = in.nextInt();

		for(int i = 1; i<n-1; i++) {
			boolean dontMax = (p[i] < Math.max(p[i-1], p[i+1]));
			boolean dontMin = (p[i] > Math.min(p[i-1], p[i+1]));
			if(dontMax && dontMin)
				ans++;

		}

		System.out.println(ans);
	} main {
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();
		int[] p = new int[n];
		int ans = 0;

		for(int i = 0; i < n; i++)
			p[i] = in.nextInt();

		for(int i = 1; i<n-1; i++) {
			boolean dontMax = (p[i] < Math.max(p[i-1], p[i+1]));
			boolean dontMin = (p[i] > Math.min(p[i-1], p[i+1]));
			if(dontMax && dontMin)
				ans++;

		}

		System.out.println(ans);
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) int n = in.nextInt(); n in.nextInt() in.nextInt in int[] p = new int[n]; p new int[n] n int ans = 0; ans 0 for(int i = 0; i < n; i++)
			p[i] = in.nextInt(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i p[i] = in.nextInt(); p[i] = in.nextInt() p[i] p i in.nextInt() in.nextInt in for(int i = 1; i<n-1; i++) {
			boolean dontMax = (p[i] < Math.max(p[i-1], p[i+1]));
			boolean dontMin = (p[i] > Math.min(p[i-1], p[i+1]));
			if(dontMax && dontMin)
				ans++;

		} int i = 1; int i = 1; i 1 i<n-1 i n-1 n 1 i++ i++ i {
			boolean dontMax = (p[i] < Math.max(p[i-1], p[i+1]));
			boolean dontMin = (p[i] > Math.min(p[i-1], p[i+1]));
			if(dontMax && dontMin)
				ans++;

		} {
			boolean dontMax = (p[i] < Math.max(p[i-1], p[i+1]));
			boolean dontMin = (p[i] > Math.min(p[i-1], p[i+1]));
			if(dontMax && dontMin)
				ans++;

		} boolean dontMax = (p[i] < Math.max(p[i-1], p[i+1])); dontMax (p[i] < Math.max(p[i-1], p[i+1])) p[i] p i Math.max(p[i-1], p[i+1]) Math.max Math p[i-1] p i-1 i 1 p[i+1] p i+1 i 1 boolean dontMin = (p[i] > Math.min(p[i-1], p[i+1])); dontMin (p[i] > Math.min(p[i-1], p[i+1])) p[i] p i Math.min(p[i-1], p[i+1]) Math.min Math p[i-1] p i-1 i 1 p[i+1] p i+1 i 1 if(dontMax && dontMin)
				ans++; dontMax && dontMin dontMax dontMin ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {

	public static void main(String[] args){
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();
		int[] p = new int[n];
		int ans = 0;

		for(int i = 0; i < n; i++)
			p[i] = in.nextInt();

		for(int i = 1; i<n-1; i++) {
			boolean dontMax = (p[i] < Math.max(p[i-1], p[i+1]));
			boolean dontMin = (p[i] > Math.min(p[i-1], p[i+1]));
			if(dontMax && dontMin)
				ans++;

		}

		System.out.println(ans);
	}

} public class Main {

	public static void main(String[] args){
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();
		int[] p = new int[n];
		int ans = 0;

		for(int i = 0; i < n; i++)
			p[i] = in.nextInt();

		for(int i = 1; i<n-1; i++) {
			boolean dontMax = (p[i] < Math.max(p[i-1], p[i+1]));
			boolean dontMin = (p[i] > Math.min(p[i-1], p[i+1]));
			if(dontMax && dontMin)
				ans++;

		}

		System.out.println(ans);
	}

} Main

import java.util.Scanner;

public class Main {

	public static void main(String[] args){
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();
		int[] p = new int[n];
		int ans = 0;

		for(int i = 0; i < n; i++)
			p[i] = in.nextInt();

		for(int i = 1; i<n-1; i++) {
			boolean dontMax = (p[i] < Math.max(p[i-1], p[i+1]));
			boolean dontMin = (p[i] > Math.min(p[i-1], p[i+1]));
			if(dontMax && dontMin)
				ans++;

		}

		System.out.println(ans);
	}

}