import java.util.*;

public class Main {
	Scanner sc = new Scanner(System.in);
	final int MOD = 1000000007;
	final int MAX = Integer.MAX_VALUE;
	final long LMAX = Long.MAX_VALUE;
	final int LEN = 100000;

	void doIt() {
		int n = sc.nextInt();
		int p[] = new int[n];
		for(int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 1; i < n - 1; i++) {
			if(p[i - 1] < p[i] && p[i] < p[i + 1]) ans++;
			else if(p[i - 1] > p[i] && p[i] > p[i + 1])ans++;
		}
		System.out.println(ans);
		
	}
	public static void main(String[] args) {
		new Main().doIt();
	}
} import java.util.*; util.* java public class Main {
	Scanner sc = new Scanner(System.in);
	final int MOD = 1000000007;
	final int MAX = Integer.MAX_VALUE;
	final long LMAX = Long.MAX_VALUE;
	final int LEN = 100000;

	void doIt() {
		int n = sc.nextInt();
		int p[] = new int[n];
		for(int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 1; i < n - 1; i++) {
			if(p[i - 1] < p[i] && p[i] < p[i + 1]) ans++;
			else if(p[i - 1] > p[i] && p[i] > p[i + 1])ans++;
		}
		System.out.println(ans);
		
	}
	public static void main(String[] args) {
		new Main().doIt();
	}
} Main Scanner sc = new Scanner(System.in); sc new Scanner(System.in) final int MOD = 1000000007; MOD 1000000007 final int MAX = Integer.MAX_VALUE; MAX Integer.MAX_VALUE Integer Integer.MAX_VALUE final long LMAX = Long.MAX_VALUE; LMAX Long.MAX_VALUE Long Long.MAX_VALUE final int LEN = 100000; LEN 100000 void doIt() {
		int n = sc.nextInt();
		int p[] = new int[n];
		for(int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 1; i < n - 1; i++) {
			if(p[i - 1] < p[i] && p[i] < p[i + 1]) ans++;
			else if(p[i - 1] > p[i] && p[i] > p[i + 1])ans++;
		}
		System.out.println(ans);
		
	} doIt {
		int n = sc.nextInt();
		int p[] = new int[n];
		for(int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 1; i < n - 1; i++) {
			if(p[i - 1] < p[i] && p[i] < p[i + 1]) ans++;
			else if(p[i - 1] > p[i] && p[i] > p[i + 1])ans++;
		}
		System.out.println(ans);
		
	} int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int p[] = new int[n]; p new int[n] n for(int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			p[i] = sc.nextInt();
		} {
			p[i] = sc.nextInt();
		} p[i] = sc.nextInt() p[i] p i sc.nextInt() sc.nextInt sc int ans = 0; ans 0 for(int i = 1; i < n - 1; i++) {
			if(p[i - 1] < p[i] && p[i] < p[i + 1]) ans++;
			else if(p[i - 1] > p[i] && p[i] > p[i + 1])ans++;
		} int i = 1; int i = 1; i 1 i < n - 1 i n - 1 n 1 i++ i++ i {
			if(p[i - 1] < p[i] && p[i] < p[i + 1]) ans++;
			else if(p[i - 1] > p[i] && p[i] > p[i + 1])ans++;
		} {
			if(p[i - 1] < p[i] && p[i] < p[i + 1]) ans++;
			else if(p[i - 1] > p[i] && p[i] > p[i + 1])ans++;
		} if(p[i - 1] < p[i] && p[i] < p[i + 1]) ans++;
			else if(p[i - 1] > p[i] && p[i] > p[i + 1])ans++; p[i - 1] < p[i] && p[i] < p[i + 1] p[i - 1] < p[i] p[i - 1] p i - 1 i 1 p[i] p i p[i] < p[i + 1] p[i] p i p[i + 1] p i + 1 i 1 ans++ ans if(p[i - 1] > p[i] && p[i] > p[i + 1])ans++; p[i - 1] > p[i] && p[i] > p[i + 1] p[i - 1] > p[i] p[i - 1] p i - 1 i 1 p[i] p i p[i] > p[i + 1] p[i] p i p[i + 1] p i + 1 i 1 ans++ ans System.out.println(ans) System.out.println System.out System System.out ans public static void main(String[] args) {
		new Main().doIt();
	} main {
		new Main().doIt();
	} new Main().doIt() new Main().doIt new Main() String[] args args public class Main {
	Scanner sc = new Scanner(System.in);
	final int MOD = 1000000007;
	final int MAX = Integer.MAX_VALUE;
	final long LMAX = Long.MAX_VALUE;
	final int LEN = 100000;

	void doIt() {
		int n = sc.nextInt();
		int p[] = new int[n];
		for(int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 1; i < n - 1; i++) {
			if(p[i - 1] < p[i] && p[i] < p[i + 1]) ans++;
			else if(p[i - 1] > p[i] && p[i] > p[i + 1])ans++;
		}
		System.out.println(ans);
		
	}
	public static void main(String[] args) {
		new Main().doIt();
	}
} public class Main {
	Scanner sc = new Scanner(System.in);
	final int MOD = 1000000007;
	final int MAX = Integer.MAX_VALUE;
	final long LMAX = Long.MAX_VALUE;
	final int LEN = 100000;

	void doIt() {
		int n = sc.nextInt();
		int p[] = new int[n];
		for(int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 1; i < n - 1; i++) {
			if(p[i - 1] < p[i] && p[i] < p[i + 1]) ans++;
			else if(p[i - 1] > p[i] && p[i] > p[i + 1])ans++;
		}
		System.out.println(ans);
		
	}
	public static void main(String[] args) {
		new Main().doIt();
	}
} Main
import java.util.*;

public class Main {
	Scanner sc = new Scanner(System.in);
	final int MOD = 1000000007;
	final int MAX = Integer.MAX_VALUE;
	final long LMAX = Long.MAX_VALUE;
	final int LEN = 100000;

	void doIt() {
		int n = sc.nextInt();
		int p[] = new int[n];
		for(int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 1; i < n - 1; i++) {
			if(p[i - 1] < p[i] && p[i] < p[i + 1]) ans++;
			else if(p[i - 1] > p[i] && p[i] > p[i + 1])ans++;
		}
		System.out.println(ans);
		
	}
	public static void main(String[] args) {
		new Main().doIt();
	}
}
