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