import java.util.*;

public class Main {
	public static void main(String[] args) {
		Main main = new Main();
		main.run();
	}

public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int p[] = new int[n];
		for(int i=0; i<n; i++) p[i] = sc.nextInt();
		int cnt=0;
		for(int i=1; i<n-1; i++) {
			if(p[i-1] < p[i] && p[i] < p[i+1] || p[i-1] > p[i] && p[i] > p[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
		sc.close();
	}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args) {
		Main main = new Main();
		main.run();
	}

public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int p[] = new int[n];
		for(int i=0; i<n; i++) p[i] = sc.nextInt();
		int cnt=0;
		for(int i=1; i<n-1; i++) {
			if(p[i-1] < p[i] && p[i] < p[i+1] || p[i-1] > p[i] && p[i] > p[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
		sc.close();
	}
} Main public static void main(String[] args) {
		Main main = new Main();
		main.run();
	} main {
		Main main = new Main();
		main.run();
	} Main main = new Main(); main new Main() main.run() main.run main String[] args args public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int p[] = new int[n];
		for(int i=0; i<n; i++) p[i] = sc.nextInt();
		int cnt=0;
		for(int i=1; i<n-1; i++) {
			if(p[i-1] < p[i] && p[i] < p[i+1] || p[i-1] > p[i] && p[i] > p[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
		sc.close();
	} run {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int p[] = new int[n];
		for(int i=0; i<n; i++) p[i] = sc.nextInt();
		int cnt=0;
		for(int i=1; i<n-1; i++) {
			if(p[i-1] < p[i] && p[i] < p[i+1] || p[i-1] > p[i] && p[i] > p[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
		sc.close();
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) 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] p i sc.nextInt() sc.nextInt sc int cnt=0; cnt 0 for(int i=1; i<n-1; i++) {
			if(p[i-1] < p[i] && p[i] < p[i+1] || p[i-1] > p[i] && p[i] > p[i+1]) {
				cnt++;
			}
		} 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] || p[i-1] > p[i] && p[i] > p[i+1]) {
				cnt++;
			}
		} {
			if(p[i-1] < p[i] && p[i] < p[i+1] || p[i-1] > p[i] && p[i] > p[i+1]) {
				cnt++;
			}
		} if(p[i-1] < p[i] && p[i] < p[i+1] || p[i-1] > p[i] && p[i] > p[i+1]) {
				cnt++;
			} p[i-1] < p[i] && p[i] < p[i+1] || p[i-1] > p[i] && p[i] > p[i+1] 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 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 {
				cnt++;
			} cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt sc.close() sc.close sc public class Main {
	public static void main(String[] args) {
		Main main = new Main();
		main.run();
	}

public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int p[] = new int[n];
		for(int i=0; i<n; i++) p[i] = sc.nextInt();
		int cnt=0;
		for(int i=1; i<n-1; i++) {
			if(p[i-1] < p[i] && p[i] < p[i+1] || p[i-1] > p[i] && p[i] > p[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
		sc.close();
	}
} public class Main {
	public static void main(String[] args) {
		Main main = new Main();
		main.run();
	}

public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int p[] = new int[n];
		for(int i=0; i<n; i++) p[i] = sc.nextInt();
		int cnt=0;
		for(int i=1; i<n-1; i++) {
			if(p[i-1] < p[i] && p[i] < p[i+1] || p[i-1] > p[i] && p[i] > p[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
		sc.close();
	}
} Main
import java.util.*;

public class Main {
	public static void main(String[] args) {
		Main main = new Main();
		main.run();
	}

public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int p[] = new int[n];
		for(int i=0; i<n; i++) p[i] = sc.nextInt();
		int cnt=0;
		for(int i=1; i<n-1; i++) {
			if(p[i-1] < p[i] && p[i] < p[i+1] || p[i-1] > p[i] && p[i] > p[i+1]) {
				cnt++;
			}
		}
		System.out.println(cnt);
		sc.close();
	}
}
