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