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

    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[]p = new int[n];
    
    int cou = 0;
    for(int i=0; i<n; i++) {
    	p[i] = sc.nextInt();
    }
    for(int i=0; i<n-2; i++) {
    	if(p[i+1]<p[i] && p[i+1]>=p[i+2]) {
    			cou++;
    	}
    		if(p[i+1]>=p[i] && p[i+1]<p[i+2]) {
    	    	cou++;
    	}
    }
    		System.out.println(cou);
      } main {

    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[]p = new int[n];
    
    int cou = 0;
    for(int i=0; i<n; i++) {
    	p[i] = sc.nextInt();
    }
    for(int i=0; i<n-2; i++) {
    	if(p[i+1]<p[i] && p[i+1]>=p[i+2]) {
    			cou++;
    	}
    		if(p[i+1]>=p[i] && p[i+1]<p[i+2]) {
    	    	cou++;
    	}
    }
    		System.out.println(cou);
      } 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 cou = 0; cou 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=0; i<n-2; i++) {
    	if(p[i+1]<p[i] && p[i+1]>=p[i+2]) {
    			cou++;
    	}
    		if(p[i+1]>=p[i] && p[i+1]<p[i+2]) {
    	    	cou++;
    	}
    } int i=0; int i=0; i 0 i<n-2 i n-2 n 2 i++ i++ i {
    	if(p[i+1]<p[i] && p[i+1]>=p[i+2]) {
    			cou++;
    	}
    		if(p[i+1]>=p[i] && p[i+1]<p[i+2]) {
    	    	cou++;
    	}
    } {
    	if(p[i+1]<p[i] && p[i+1]>=p[i+2]) {
    			cou++;
    	}
    		if(p[i+1]>=p[i] && p[i+1]<p[i+2]) {
    	    	cou++;
    	}
    } if(p[i+1]<p[i] && p[i+1]>=p[i+2]) {
    			cou++;
    	} p[i+1]<p[i] && p[i+1]>=p[i+2] p[i+1]<p[i] p[i+1] p i+1 i 1 p[i] p i p[i+1]>=p[i+2] p[i+1] p i+1 i 1 p[i+2] p i+2 i 2 {
    			cou++;
    	} cou++ cou if(p[i+1]>=p[i] && p[i+1]<p[i+2]) {
    	    	cou++;
    	} p[i+1]>=p[i] && p[i+1]<p[i+2] p[i+1]>=p[i] p[i+1] p i+1 i 1 p[i] p i p[i+1]<p[i+2] p[i+1] p i+1 i 1 p[i+2] p i+2 i 2 {
    	    	cou++;
    	} cou++ cou System.out.println(cou) System.out.println System.out System System.out cou 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 cou = 0;
    for(int i=0; i<n; i++) {
    	p[i] = sc.nextInt();
    }
    for(int i=0; i<n-2; i++) {
    	if(p[i+1]<p[i] && p[i+1]>=p[i+2]) {
    			cou++;
    	}
    		if(p[i+1]>=p[i] && p[i+1]<p[i+2]) {
    	    	cou++;
    	}
    }
    		System.out.println(cou);
      }
} 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 cou = 0;
    for(int i=0; i<n; i++) {
    	p[i] = sc.nextInt();
    }
    for(int i=0; i<n-2; i++) {
    	if(p[i+1]<p[i] && p[i+1]>=p[i+2]) {
    			cou++;
    	}
    		if(p[i+1]>=p[i] && p[i+1]<p[i+2]) {
    	    	cou++;
    	}
    }
    		System.out.println(cou);
      }
} Main
import java.util.Scanner;
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 cou = 0;
    for(int i=0; i<n; i++) {
    	p[i] = sc.nextInt();
    }
    for(int i=0; i<n-2; i++) {
    	if(p[i+1]<p[i] && p[i+1]>=p[i+2]) {
    			cou++;
    	}
    		if(p[i+1]>=p[i] && p[i+1]<p[i+2]) {
    	    	cou++;
    	}
    }
    		System.out.println(cou);
      }
}
