import 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];

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

        int ans = 0;
        for(int i=0; i<n; i++){
		p[i] = sc.nextInt();
}
        for(int i=1; i<n-1; i++){ 
        if(p[i]>=p[i-1] && p[i]<p[i+1]){
            ans++;
        }else if(p[i]<p[i-1] && p[i]>=p[i+1]){    
            ans++;
    }
}
        System.out.print(ans);    
        }
} Main public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[]p = new int[n];

        int ans = 0;
        for(int i=0; i<n; i++){
		p[i] = sc.nextInt();
}
        for(int i=1; i<n-1; i++){ 
        if(p[i]>=p[i-1] && p[i]<p[i+1]){
            ans++;
        }else if(p[i]<p[i-1] && p[i]>=p[i+1]){    
            ans++;
    }
}
        System.out.print(ans);    
        } main {
    
    Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[]p = new int[n];

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

        int ans = 0;
        for(int i=0; i<n; i++){
		p[i] = sc.nextInt();
}
        for(int i=1; i<n-1; i++){ 
        if(p[i]>=p[i-1] && p[i]<p[i+1]){
            ans++;
        }else if(p[i]<p[i-1] && p[i]>=p[i+1]){    
            ans++;
    }
}
        System.out.print(ans);    
        }
} public class Main {
	public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[]p = new int[n];

        int ans = 0;
        for(int i=0; i<n; i++){
		p[i] = sc.nextInt();
}
        for(int i=1; i<n-1; i++){ 
        if(p[i]>=p[i-1] && p[i]<p[i+1]){
            ans++;
        }else if(p[i]<p[i-1] && p[i]>=p[i+1]){    
            ans++;
    }
}
        System.out.print(ans);    
        }
} Main
import 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];

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