import java.util.Scanner;
public class Main {
	public static void main(String[] args) {	
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int p[]=new int[n];
		int cnt=0;	
		for(int i=0;i<n;i++) {p[i]=sc.nextInt();}
		for(int i=0;i<n-2;i++) {
			int a=p[i];
			int b=p[i+1];
			int c=p[i+2];
			int mid = -9999;
			if(a > b && a < c || a > c && a < b || a == b || a == c )
			mid = a;
			else if(b > a && b < c || b > c && b < a || b == a || b == c )
			mid = b;
			else
			mid =c ;
			if(b==mid)cnt++;
		}
		System.out.println(cnt);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {	
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int p[]=new int[n];
		int cnt=0;	
		for(int i=0;i<n;i++) {p[i]=sc.nextInt();}
		for(int i=0;i<n-2;i++) {
			int a=p[i];
			int b=p[i+1];
			int c=p[i+2];
			int mid = -9999;
			if(a > b && a < c || a > c && a < b || a == b || a == c )
			mid = a;
			else if(b > a && b < c || b > c && b < a || b == a || b == c )
			mid = b;
			else
			mid =c ;
			if(b==mid)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];
		int cnt=0;	
		for(int i=0;i<n;i++) {p[i]=sc.nextInt();}
		for(int i=0;i<n-2;i++) {
			int a=p[i];
			int b=p[i+1];
			int c=p[i+2];
			int mid = -9999;
			if(a > b && a < c || a > c && a < b || a == b || a == c )
			mid = a;
			else if(b > a && b < c || b > c && b < a || b == a || b == c )
			mid = b;
			else
			mid =c ;
			if(b==mid)cnt++;
		}
		System.out.println(cnt);
	} main {	
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int p[]=new int[n];
		int cnt=0;	
		for(int i=0;i<n;i++) {p[i]=sc.nextInt();}
		for(int i=0;i<n-2;i++) {
			int a=p[i];
			int b=p[i+1];
			int c=p[i+2];
			int mid = -9999;
			if(a > b && a < c || a > c && a < b || a == b || a == c )
			mid = a;
			else if(b > a && b < c || b > c && b < a || b == a || b == c )
			mid = b;
			else
			mid =c ;
			if(b==mid)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 int cnt=0; cnt 0 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 for(int i=0;i<n-2;i++) {
			int a=p[i];
			int b=p[i+1];
			int c=p[i+2];
			int mid = -9999;
			if(a > b && a < c || a > c && a < b || a == b || a == c )
			mid = a;
			else if(b > a && b < c || b > c && b < a || b == a || b == c )
			mid = b;
			else
			mid =c ;
			if(b==mid)cnt++;
		} int i=0; int i=0; i 0 i<n-2 i n-2 n 2 i++ i++ i {
			int a=p[i];
			int b=p[i+1];
			int c=p[i+2];
			int mid = -9999;
			if(a > b && a < c || a > c && a < b || a == b || a == c )
			mid = a;
			else if(b > a && b < c || b > c && b < a || b == a || b == c )
			mid = b;
			else
			mid =c ;
			if(b==mid)cnt++;
		} {
			int a=p[i];
			int b=p[i+1];
			int c=p[i+2];
			int mid = -9999;
			if(a > b && a < c || a > c && a < b || a == b || a == c )
			mid = a;
			else if(b > a && b < c || b > c && b < a || b == a || b == c )
			mid = b;
			else
			mid =c ;
			if(b==mid)cnt++;
		} int a=p[i]; a p[i] p i int b=p[i+1]; b p[i+1] p i+1 i 1 int c=p[i+2]; c p[i+2] p i+2 i 2 int mid = -9999; mid -9999 9999 if(a > b && a < c || a > c && a < b || a == b || a == c )
			mid = a;
			else if(b > a && b < c || b > c && b < a || b == a || b == c )
			mid = b;
			else
			mid =c ; a > b && a < c || a > c && a < b || a == b || a == c a == b a > b && a < c || a > c && a < b || a == b || a == c a > b && a < c a > b a b a < c a c a > c && a < b a > c a c a < b a b a == b a b a == c a c mid = a mid a if(b > a && b < c || b > c && b < a || b == a || b == c )
			mid = b;
			else
			mid =c ; b > a && b < c || b > c && b < a || b == a || b == c b == a b > a && b < c || b > c && b < a || b == a || b == c b > a && b < c b > a b a b < c b c b > c && b < a b > c b c b < a b a b == a b a b == c b c mid = b mid b mid =c mid c if(b==mid)cnt++; b==mid b mid cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args public class Main {
	public static void main(String[] args) {	
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int p[]=new int[n];
		int cnt=0;	
		for(int i=0;i<n;i++) {p[i]=sc.nextInt();}
		for(int i=0;i<n-2;i++) {
			int a=p[i];
			int b=p[i+1];
			int c=p[i+2];
			int mid = -9999;
			if(a > b && a < c || a > c && a < b || a == b || a == c )
			mid = a;
			else if(b > a && b < c || b > c && b < a || b == a || b == c )
			mid = b;
			else
			mid =c ;
			if(b==mid)cnt++;
		}
		System.out.println(cnt);
	}
} public class Main {
	public static void main(String[] args) {	
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int p[]=new int[n];
		int cnt=0;	
		for(int i=0;i<n;i++) {p[i]=sc.nextInt();}
		for(int i=0;i<n-2;i++) {
			int a=p[i];
			int b=p[i+1];
			int c=p[i+2];
			int mid = -9999;
			if(a > b && a < c || a > c && a < b || a == b || a == c )
			mid = a;
			else if(b > a && b < c || b > c && b < a || b == a || b == c )
			mid = b;
			else
			mid =c ;
			if(b==mid)cnt++;
		}
		System.out.println(cnt);
	}
} Main
import java.util.Scanner;
public class Main {
	public static void main(String[] args) {	
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int p[]=new int[n];
		int cnt=0;	
		for(int i=0;i<n;i++) {p[i]=sc.nextInt();}
		for(int i=0;i<n-2;i++) {
			int a=p[i];
			int b=p[i+1];
			int c=p[i+2];
			int mid = -9999;
			if(a > b && a < c || a > c && a < b || a == b || a == c )
			mid = a;
			else if(b > a && b < c || b > c && b < a || b == a || b == c )
			mid = b;
			else
			mid =c ;
			if(b==mid)cnt++;
		}
		System.out.println(cnt);
	}
}