import java.util.Scanner;


import java.util.Comparator;
import java.util.Arrays;
import java.util.ArrayList;



public 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 sum = 0;
		for(int i = 0; i<n-2 ;i++) {
			if(p[i] < p[i+1] && p[i+1]<p[i+2]) {
				sum++;
			}
			else if(p[i] > p[i+1] && p[i+1] > p[i+2]) {
				sum++;
			}
		}
		System.out.println(sum);

		
	}
} import java.util.Scanner; Scanner java.util import java.util.Comparator; Comparator java.util import java.util.Arrays; Arrays java.util import java.util.ArrayList; ArrayList 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];
		for(int i = 0; i<n ;i++) {
			p[i] = sc.nextInt();
		}
		int sum = 0;
		for(int i = 0; i<n-2 ;i++) {
			if(p[i] < p[i+1] && p[i+1]<p[i+2]) {
				sum++;
			}
			else if(p[i] > p[i+1] && p[i+1] > p[i+2]) {
				sum++;
			}
		}
		System.out.println(sum);

		
	}
} 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 sum = 0;
		for(int i = 0; i<n-2 ;i++) {
			if(p[i] < p[i+1] && p[i+1]<p[i+2]) {
				sum++;
			}
			else if(p[i] > p[i+1] && p[i+1] > p[i+2]) {
				sum++;
			}
		}
		System.out.println(sum);

		
	} 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 sum = 0;
		for(int i = 0; i<n-2 ;i++) {
			if(p[i] < p[i+1] && p[i+1]<p[i+2]) {
				sum++;
			}
			else if(p[i] > p[i+1] && p[i+1] > p[i+2]) {
				sum++;
			}
		}
		System.out.println(sum);

		
	} 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 sum = 0; sum 0 for(int i = 0; i<n-2 ;i++) {
			if(p[i] < p[i+1] && p[i+1]<p[i+2]) {
				sum++;
			}
			else if(p[i] > p[i+1] && p[i+1] > p[i+2]) {
				sum++;
			}
		} 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]) {
				sum++;
			}
			else if(p[i] > p[i+1] && p[i+1] > p[i+2]) {
				sum++;
			}
		} {
			if(p[i] < p[i+1] && p[i+1]<p[i+2]) {
				sum++;
			}
			else if(p[i] > p[i+1] && p[i+1] > p[i+2]) {
				sum++;
			}
		} if(p[i] < p[i+1] && p[i+1]<p[i+2]) {
				sum++;
			}
			else if(p[i] > p[i+1] && p[i+1] > p[i+2]) {
				sum++;
			} 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 {
				sum++;
			} sum++ sum if(p[i] > p[i+1] && p[i+1] > p[i+2]) {
				sum++;
			} 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 {
				sum++;
			} sum++ sum System.out.println(sum) System.out.println System.out System System.out sum 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];
		for(int i = 0; i<n ;i++) {
			p[i] = sc.nextInt();
		}
		int sum = 0;
		for(int i = 0; i<n-2 ;i++) {
			if(p[i] < p[i+1] && p[i+1]<p[i+2]) {
				sum++;
			}
			else if(p[i] > p[i+1] && p[i+1] > p[i+2]) {
				sum++;
			}
		}
		System.out.println(sum);

		
	}
} public 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 sum = 0;
		for(int i = 0; i<n-2 ;i++) {
			if(p[i] < p[i+1] && p[i+1]<p[i+2]) {
				sum++;
			}
			else if(p[i] > p[i+1] && p[i+1] > p[i+2]) {
				sum++;
			}
		}
		System.out.println(sum);

		
	}
} Main
import java.util.Scanner;


import java.util.Comparator;
import java.util.Arrays;
import java.util.ArrayList;



public 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 sum = 0;
		for(int i = 0; i<n-2 ;i++) {
			if(p[i] < p[i+1] && p[i+1]<p[i+2]) {
				sum++;
			}
			else if(p[i] > p[i+1] && p[i+1] > p[i+2]) {
				sum++;
			}
		}
		System.out.println(sum);

		
	}
}
