import java.util.*;
import java.math.*;
public class Main {
    static final int MOD = 1_000_000_007; // 10^9+7
    //static final int MAX = 2_147_483_646; // intの最大値
    static final int INF = 1_000_000_000; // 10^9
    static final int MAX = 10_000_000;
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] ary = new int[n];
        for(int i = 0;i < n;i++){
            ary[i] = sc.nextInt();
        }
        int ans = 0;
        for(int i = 0;i < n-2;i++){
            if(ary[i] < ary[i+1]&&ary[i+1] < ary[i+2])ans++;
            if(ary[i] > ary[i+1]&&ary[i+1] > ary[i+2])ans++;
        }
        System.out.println(ans);
    }       
}



 import java.util.*; util.* java import java.math.*; math.* java public class Main {
    static final int MOD = 1_000_000_007; // 10^9+7
    //static final int MAX = 2_147_483_646; // intの最大値
    static final int INF = 1_000_000_000; // 10^9
    static final int MAX = 10_000_000;
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] ary = new int[n];
        for(int i = 0;i < n;i++){
            ary[i] = sc.nextInt();
        }
        int ans = 0;
        for(int i = 0;i < n-2;i++){
            if(ary[i] < ary[i+1]&&ary[i+1] < ary[i+2])ans++;
            if(ary[i] > ary[i+1]&&ary[i+1] > ary[i+2])ans++;
        }
        System.out.println(ans);
    }       
} Main static final int MOD = 1_000_000_007; // 10^9+7 MOD 1_000_000_007 //static final int MAX = 2_147_483_646; // intの最大値
    static final int INF = 1_000_000_000; // 10^9 INF 1_000_000_000 static final int MAX = 10_000_000; MAX 10_000_000 public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] ary = new int[n];
        for(int i = 0;i < n;i++){
            ary[i] = sc.nextInt();
        }
        int ans = 0;
        for(int i = 0;i < n-2;i++){
            if(ary[i] < ary[i+1]&&ary[i+1] < ary[i+2])ans++;
            if(ary[i] > ary[i+1]&&ary[i+1] > ary[i+2])ans++;
        }
        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] ary = new int[n];
        for(int i = 0;i < n;i++){
            ary[i] = sc.nextInt();
        }
        int ans = 0;
        for(int i = 0;i < n-2;i++){
            if(ary[i] < ary[i+1]&&ary[i+1] < ary[i+2])ans++;
            if(ary[i] > ary[i+1]&&ary[i+1] > ary[i+2])ans++;
        }
        System.out.println(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] ary = new int[n]; ary new int[n] n for(int i = 0;i < n;i++){
            ary[i] = sc.nextInt();
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            ary[i] = sc.nextInt();
        } {
            ary[i] = sc.nextInt();
        } ary[i] = sc.nextInt() ary[i] ary i sc.nextInt() sc.nextInt sc int ans = 0; ans 0 for(int i = 0;i < n-2;i++){
            if(ary[i] < ary[i+1]&&ary[i+1] < ary[i+2])ans++;
            if(ary[i] > ary[i+1]&&ary[i+1] > ary[i+2])ans++;
        } int i = 0; int i = 0; i 0 i < n-2 i n-2 n 2 i++ i++ i {
            if(ary[i] < ary[i+1]&&ary[i+1] < ary[i+2])ans++;
            if(ary[i] > ary[i+1]&&ary[i+1] > ary[i+2])ans++;
        } {
            if(ary[i] < ary[i+1]&&ary[i+1] < ary[i+2])ans++;
            if(ary[i] > ary[i+1]&&ary[i+1] > ary[i+2])ans++;
        } if(ary[i] < ary[i+1]&&ary[i+1] < ary[i+2])ans++; ary[i] < ary[i+1]&&ary[i+1] < ary[i+2] ary[i] < ary[i+1] ary[i] ary i ary[i+1] ary i+1 i 1 ary[i+1] < ary[i+2] ary[i+1] ary i+1 i 1 ary[i+2] ary i+2 i 2 ans++ ans if(ary[i] > ary[i+1]&&ary[i+1] > ary[i+2])ans++; ary[i] > ary[i+1]&&ary[i+1] > ary[i+2] ary[i] > ary[i+1] ary[i] ary i ary[i+1] ary i+1 i 1 ary[i+1] > ary[i+2] ary[i+1] ary i+1 i 1 ary[i+2] ary i+2 i 2 ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String args[] args public class Main {
    static final int MOD = 1_000_000_007; // 10^9+7
    //static final int MAX = 2_147_483_646; // intの最大値
    static final int INF = 1_000_000_000; // 10^9
    static final int MAX = 10_000_000;
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] ary = new int[n];
        for(int i = 0;i < n;i++){
            ary[i] = sc.nextInt();
        }
        int ans = 0;
        for(int i = 0;i < n-2;i++){
            if(ary[i] < ary[i+1]&&ary[i+1] < ary[i+2])ans++;
            if(ary[i] > ary[i+1]&&ary[i+1] > ary[i+2])ans++;
        }
        System.out.println(ans);
    }       
} public class Main {
    static final int MOD = 1_000_000_007; // 10^9+7
    //static final int MAX = 2_147_483_646; // intの最大値
    static final int INF = 1_000_000_000; // 10^9
    static final int MAX = 10_000_000;
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] ary = new int[n];
        for(int i = 0;i < n;i++){
            ary[i] = sc.nextInt();
        }
        int ans = 0;
        for(int i = 0;i < n-2;i++){
            if(ary[i] < ary[i+1]&&ary[i+1] < ary[i+2])ans++;
            if(ary[i] > ary[i+1]&&ary[i+1] > ary[i+2])ans++;
        }
        System.out.println(ans);
    }       
} Main
import java.util.*;
import java.math.*;
public class Main {
    static final int MOD = 1_000_000_007; // 10^9+7
    //static final int MAX = 2_147_483_646; // intの最大値
    static final int INF = 1_000_000_000; // 10^9
    static final int MAX = 10_000_000;
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] ary = new int[n];
        for(int i = 0;i < n;i++){
            ary[i] = sc.nextInt();
        }
        int ans = 0;
        for(int i = 0;i < n-2;i++){
            if(ary[i] < ary[i+1]&&ary[i+1] < ary[i+2])ans++;
            if(ary[i] > ary[i+1]&&ary[i+1] > ary[i+2])ans++;
        }
        System.out.println(ans);
    }       
}




