import java.util.Scanner;

class Main{
	public static void main(String[] args){
		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 + 1 < n; i++) {
			int max = Math.max(Math.max(p[i], p[i + 1]), p[i - 1]);
			int min = Math.min(Math.min(p[i], p[i + 1]), p[i - 1]);
			int mid = p[i] ^ p[i + 1] ^ p[i - 1] ^ max ^ min;
			if(mid == p[i]) cnt++;
		}
		System.out.println(cnt);
	}
} import java.util.Scanner; Scanner java.util class Main{
	public static void main(String[] args){
		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 + 1 < n; i++) {
			int max = Math.max(Math.max(p[i], p[i + 1]), p[i - 1]);
			int min = Math.min(Math.min(p[i], p[i + 1]), p[i - 1]);
			int mid = p[i] ^ p[i + 1] ^ p[i - 1] ^ max ^ min;
			if(mid == p[i]) cnt++;
		}
		System.out.println(cnt);
	}
} Main public static void main(String[] args){
		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 + 1 < n; i++) {
			int max = Math.max(Math.max(p[i], p[i + 1]), p[i - 1]);
			int min = Math.min(Math.min(p[i], p[i + 1]), p[i - 1]);
			int mid = p[i] ^ p[i + 1] ^ p[i - 1] ^ max ^ min;
			if(mid == p[i]) cnt++;
		}
		System.out.println(cnt);
	} main {
		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 + 1 < n; i++) {
			int max = Math.max(Math.max(p[i], p[i + 1]), p[i - 1]);
			int min = Math.min(Math.min(p[i], p[i + 1]), p[i - 1]);
			int mid = p[i] ^ p[i + 1] ^ p[i - 1] ^ max ^ min;
			if(mid == p[i]) cnt++;
		}
		System.out.println(cnt);
	} 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 + 1 < n; i++) {
			int max = Math.max(Math.max(p[i], p[i + 1]), p[i - 1]);
			int min = Math.min(Math.min(p[i], p[i + 1]), p[i - 1]);
			int mid = p[i] ^ p[i + 1] ^ p[i - 1] ^ max ^ min;
			if(mid == p[i]) cnt++;
		} int i = 1; int i = 1; i 1 i + 1 < n i + 1 i 1 n i++ i++ i {
			int max = Math.max(Math.max(p[i], p[i + 1]), p[i - 1]);
			int min = Math.min(Math.min(p[i], p[i + 1]), p[i - 1]);
			int mid = p[i] ^ p[i + 1] ^ p[i - 1] ^ max ^ min;
			if(mid == p[i]) cnt++;
		} {
			int max = Math.max(Math.max(p[i], p[i + 1]), p[i - 1]);
			int min = Math.min(Math.min(p[i], p[i + 1]), p[i - 1]);
			int mid = p[i] ^ p[i + 1] ^ p[i - 1] ^ max ^ min;
			if(mid == p[i]) cnt++;
		} int max = Math.max(Math.max(p[i], p[i + 1]), p[i - 1]); max Math.max(Math.max(p[i], p[i + 1]), p[i - 1]) Math.max Math Math.max(p[i], p[i + 1]) Math.max Math p[i] p i p[i + 1] p i + 1 i 1 p[i - 1] p i - 1 i 1 int min = Math.min(Math.min(p[i], p[i + 1]), p[i - 1]); min Math.min(Math.min(p[i], p[i + 1]), p[i - 1]) Math.min Math Math.min(p[i], p[i + 1]) Math.min Math p[i] p i p[i + 1] p i + 1 i 1 p[i - 1] p i - 1 i 1 int mid = p[i] ^ p[i + 1] ^ p[i - 1] ^ max ^ min; mid p[i] ^ p[i + 1] ^ p[i - 1] ^ max ^ min max p[i - 1] p[i] ^ p[i + 1] ^ p[i - 1] ^ max ^ min p[i] p i p[i + 1] p i + 1 i 1 p[i - 1] p i - 1 i 1 max min if(mid == p[i]) cnt++; mid == p[i] mid p[i] p i cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args
import java.util.Scanner;

class Main{
	public static void main(String[] args){
		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 + 1 < n; i++) {
			int max = Math.max(Math.max(p[i], p[i + 1]), p[i - 1]);
			int min = Math.min(Math.min(p[i], p[i + 1]), p[i - 1]);
			int mid = p[i] ^ p[i + 1] ^ p[i - 1] ^ max ^ min;
			if(mid == p[i]) cnt++;
		}
		System.out.println(cnt);
	}
}