import java.util.Scanner;
class Main{


	static char[][] map;

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);			//文字の入力
		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 = 0;i < n-2;i++){
			if((p[i] < p[i+1] && p[i+1] < p[i+2] )||( p[i] > p[i+1] && p[i+1] > p[i+2])){
				ans++;
			}
		}

		System.out.println(ans);


	}



	static int gcd(int a,int b){				//最大公約数を返す
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}
	static long gcd(long a,long b){
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}



	static long lcm (long a, long b) {
		long g = gcd(a,b);
		return a/g*b;
	}




}



class Pair implements Comparable{
	int from;
	int end;
	@Override
	public int compareTo(Object other) {
		Pair otherpair = (Pair)other;

		return   end- otherpair.end;
	}







	static int find(int index,int current,int[] students,int ans,int[][] memo){
		if(current == index){
			return 1;
		}

		if(memo[current][index] != 0){
			return memo[current][index];
		}

		memo[current][index] = find(index, students[current]-1, students, ans+1, memo)+1;

		return memo[current][index];
	}



	static int gcd(int a,int b){				//最大公約数を返す
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}
	static long gcd(long a,long b){
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}



	static long lcm (long a, long b) {
		long g = gcd(a,b);
		return a/g*b;
	}




}



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


	static char[][] map;

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);			//文字の入力
		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 = 0;i < n-2;i++){
			if((p[i] < p[i+1] && p[i+1] < p[i+2] )||( p[i] > p[i+1] && p[i+1] > p[i+2])){
				ans++;
			}
		}

		System.out.println(ans);


	}



	static int gcd(int a,int b){				//最大公約数を返す
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}
	static long gcd(long a,long b){
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}



	static long lcm (long a, long b) {
		long g = gcd(a,b);
		return a/g*b;
	}




} Main static char[][] map; map public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);			//文字の入力
		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 = 0;i < n-2;i++){
			if((p[i] < p[i+1] && p[i+1] < p[i+2] )||( p[i] > p[i+1] && p[i+1] > p[i+2])){
				ans++;
			}
		}

		System.out.println(ans);


	} main {
		Scanner sc = new Scanner(System.in);			//文字の入力
		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 = 0;i < n-2;i++){
			if((p[i] < p[i+1] && p[i+1] < p[i+2] )||( p[i] > p[i+1] && p[i+1] > p[i+2])){
				ans++;
			}
		}

		System.out.println(ans);


	} 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] = sc.nextInt() p[i] p i sc.nextInt() sc.nextInt sc int ans = 0; ans 0 for(int i = 0;i < n-2;i++){
			if((p[i] < p[i+1] && p[i+1] < p[i+2] )||( p[i] > p[i+1] && p[i+1] > p[i+2])){
				ans++;
			}
		} int i = 0; int i = 0; i 0 i < n-2 i n-2 n 2 i++ i++ i {
			if((p[i] < p[i+1] && p[i+1] < p[i+2] )||( p[i] > p[i+1] && p[i+1] > p[i+2])){
				ans++;
			}
		} {
			if((p[i] < p[i+1] && p[i+1] < p[i+2] )||( p[i] > p[i+1] && p[i+1] > p[i+2])){
				ans++;
			}
		} if((p[i] < p[i+1] && p[i+1] < p[i+2] )||( p[i] > p[i+1] && p[i+1] > p[i+2])){
				ans++;
			} (p[i] < p[i+1] && p[i+1] < p[i+2] )||( p[i] > p[i+1] && p[i+1] > p[i+2]) (p[i] < p[i+1] && p[i+1] < p[i+2] ) p[i] < p[i+1] p[i] p i p[i+1] p i+1 i 1 p[i+1] < p[i+2] p[i+1] p i+1 i 1 p[i+2] p i+2 i 2 ( p[i] > p[i+1] && p[i+1] > p[i+2]) p[i] > p[i+1] p[i] p i p[i+1] p i+1 i 1 p[i+1] > p[i+2] p[i+1] p i+1 i 1 p[i+2] p i+2 i 2 {
				ans++;
			} ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args static int gcd(int a,int b){				//最大公約数を返す
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	} gcd {				//最大公約数を返す
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	} if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		} b == 0 b 0 {
			return a;
		} return a; a {
			return gcd(b, a%b);
		} return gcd(b, a%b); gcd(b, a%b) gcd b a%b a b int a a int b b static long gcd(long a,long b){
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	} gcd {
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	} if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		} b == 0 b 0 {
			return a;
		} return a; a {
			return gcd(b, a%b);
		} return gcd(b, a%b); gcd(b, a%b) gcd b a%b a b long a a long b b static long lcm (long a, long b) {
		long g = gcd(a,b);
		return a/g*b;
	} lcm {
		long g = gcd(a,b);
		return a/g*b;
	} long g = gcd(a,b); g gcd(a,b) gcd a b return a/g*b; a/g*b a/g a g b long a a long b b class Pair implements Comparable{
	int from;
	int end;
	@Override
	public int compareTo(Object other) {
		Pair otherpair = (Pair)other;

		return   end- otherpair.end;
	}







	static int find(int index,int current,int[] students,int ans,int[][] memo){
		if(current == index){
			return 1;
		}

		if(memo[current][index] != 0){
			return memo[current][index];
		}

		memo[current][index] = find(index, students[current]-1, students, ans+1, memo)+1;

		return memo[current][index];
	}



	static int gcd(int a,int b){				//最大公約数を返す
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}
	static long gcd(long a,long b){
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}



	static long lcm (long a, long b) {
		long g = gcd(a,b);
		return a/g*b;
	}




} Pair int from; from int end; end @Override
	public int compareTo(Object other) {
		Pair otherpair = (Pair)other;

		return   end- otherpair.end;
	} compareTo {
		Pair otherpair = (Pair)other;

		return   end- otherpair.end;
	} Pair otherpair = (Pair)other; otherpair (Pair)other return   end- otherpair.end; end- otherpair.end end otherpair.end otherpair otherpair.end Object other other static int find(int index,int current,int[] students,int ans,int[][] memo){
		if(current == index){
			return 1;
		}

		if(memo[current][index] != 0){
			return memo[current][index];
		}

		memo[current][index] = find(index, students[current]-1, students, ans+1, memo)+1;

		return memo[current][index];
	} find {
		if(current == index){
			return 1;
		}

		if(memo[current][index] != 0){
			return memo[current][index];
		}

		memo[current][index] = find(index, students[current]-1, students, ans+1, memo)+1;

		return memo[current][index];
	} if(current == index){
			return 1;
		} current == index current index {
			return 1;
		} return 1; 1 if(memo[current][index] != 0){
			return memo[current][index];
		} memo[current][index] != 0 memo[current][index] memo[current] memo current index 0 {
			return memo[current][index];
		} return memo[current][index]; memo[current][index] memo[current] memo current index memo[current][index] = find(index, students[current]-1, students, ans+1, memo)+1 memo[current][index] memo[current] memo current index find(index, students[current]-1, students, ans+1, memo)+1 find(index, students[current]-1, students, ans+1, memo) find index students[current]-1 students[current] students current 1 students ans+1 ans 1 memo 1 return memo[current][index]; memo[current][index] memo[current] memo current index int index index int current current int[] students students int ans ans int[][] memo memo static int gcd(int a,int b){				//最大公約数を返す
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	} gcd {				//最大公約数を返す
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	} if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		} b == 0 b 0 {
			return a;
		} return a; a {
			return gcd(b, a%b);
		} return gcd(b, a%b); gcd(b, a%b) gcd b a%b a b int a a int b b static long gcd(long a,long b){
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	} gcd {
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	} if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		} b == 0 b 0 {
			return a;
		} return a; a {
			return gcd(b, a%b);
		} return gcd(b, a%b); gcd(b, a%b) gcd b a%b a b long a a long b b static long lcm (long a, long b) {
		long g = gcd(a,b);
		return a/g*b;
	} lcm {
		long g = gcd(a,b);
		return a/g*b;
	} long g = gcd(a,b); g gcd(a,b) gcd a b return a/g*b; a/g*b a/g a g b long a a long b b Comparable
import java.util.Scanner;
class Main{


	static char[][] map;

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);			//文字の入力
		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 = 0;i < n-2;i++){
			if((p[i] < p[i+1] && p[i+1] < p[i+2] )||( p[i] > p[i+1] && p[i+1] > p[i+2])){
				ans++;
			}
		}

		System.out.println(ans);


	}



	static int gcd(int a,int b){				//最大公約数を返す
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}
	static long gcd(long a,long b){
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}



	static long lcm (long a, long b) {
		long g = gcd(a,b);
		return a/g*b;
	}




}



class Pair implements Comparable{
	int from;
	int end;
	@Override
	public int compareTo(Object other) {
		Pair otherpair = (Pair)other;

		return   end- otherpair.end;
	}







	static int find(int index,int current,int[] students,int ans,int[][] memo){
		if(current == index){
			return 1;
		}

		if(memo[current][index] != 0){
			return memo[current][index];
		}

		memo[current][index] = find(index, students[current]-1, students, ans+1, memo)+1;

		return memo[current][index];
	}



	static int gcd(int a,int b){				//最大公約数を返す
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}
	static long gcd(long a,long b){
		if(b == 0){
			return a;
		}else{
			return gcd(b, a%b);
		}
	}



	static long lcm (long a, long b) {
		long g = gcd(a,b);
		return a/g*b;
	}




}




