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