import java.util.*;
import java.lang.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer n = Integer.parseInt(scanner.next());

        Integer[] p = new Integer[n];
        for(int i = 0; i < n; i++) {
            p[i] = Integer.parseInt(scanner.next());
        }

        int count = 0;
        for(int i = 1; i < n -1; i++) {
            if(p[i-1] < p[i] != p[i] > p[i+1]) {
                count++;
            }
        }

        System.out.println(count);
    }
} import java.util.*; util.* java import java.lang.*; lang.* java import java.util.stream.*; stream.* java.util public class Main {
    public static void main(String[] args) {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer n = Integer.parseInt(scanner.next());

        Integer[] p = new Integer[n];
        for(int i = 0; i < n; i++) {
            p[i] = Integer.parseInt(scanner.next());
        }

        int count = 0;
        for(int i = 1; i < n -1; i++) {
            if(p[i-1] < p[i] != p[i] > p[i+1]) {
                count++;
            }
        }

        System.out.println(count);
    }
} Main public static void main(String[] args) {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer n = Integer.parseInt(scanner.next());

        Integer[] p = new Integer[n];
        for(int i = 0; i < n; i++) {
            p[i] = Integer.parseInt(scanner.next());
        }

        int count = 0;
        for(int i = 1; i < n -1; i++) {
            if(p[i-1] < p[i] != p[i] > p[i+1]) {
                count++;
            }
        }

        System.out.println(count);
    } main {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer n = Integer.parseInt(scanner.next());

        Integer[] p = new Integer[n];
        for(int i = 0; i < n; i++) {
            p[i] = Integer.parseInt(scanner.next());
        }

        int count = 0;
        for(int i = 1; i < n -1; i++) {
            if(p[i-1] < p[i] != p[i] > p[i+1]) {
                count++;
            }
        }

        System.out.println(count);
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) Integer n = Integer.parseInt(scanner.next()); n Integer.parseInt(scanner.next()) Integer.parseInt Integer scanner.next() scanner.next scanner Integer[] p = new Integer[n]; p new Integer[n] n for(int i = 0; i < n; i++) {
            p[i] = Integer.parseInt(scanner.next());
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            p[i] = Integer.parseInt(scanner.next());
        } {
            p[i] = Integer.parseInt(scanner.next());
        } p[i] = Integer.parseInt(scanner.next()) p[i] p i Integer.parseInt(scanner.next()) Integer.parseInt Integer scanner.next() scanner.next scanner int count = 0; count 0 for(int i = 1; i < n -1; i++) {
            if(p[i-1] < p[i] != p[i] > p[i+1]) {
                count++;
            }
        } int i = 1; int i = 1; i 1 i < n -1 i n -1 n 1 i++ i++ i {
            if(p[i-1] < p[i] != p[i] > p[i+1]) {
                count++;
            }
        } {
            if(p[i-1] < p[i] != p[i] > p[i+1]) {
                count++;
            }
        } if(p[i-1] < p[i] != p[i] > p[i+1]) {
                count++;
            } p[i-1] < p[i] != p[i] > p[i+1] p[i-1] < p[i] p[i-1] p i-1 i 1 p[i] p i p[i] > p[i+1] p[i] p i p[i+1] p i+1 i 1 {
                count++;
            } 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) {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer n = Integer.parseInt(scanner.next());

        Integer[] p = new Integer[n];
        for(int i = 0; i < n; i++) {
            p[i] = Integer.parseInt(scanner.next());
        }

        int count = 0;
        for(int i = 1; i < n -1; i++) {
            if(p[i-1] < p[i] != p[i] > p[i+1]) {
                count++;
            }
        }

        System.out.println(count);
    }
} public class Main {
    public static void main(String[] args) {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer n = Integer.parseInt(scanner.next());

        Integer[] p = new Integer[n];
        for(int i = 0; i < n; i++) {
            p[i] = Integer.parseInt(scanner.next());
        }

        int count = 0;
        for(int i = 1; i < n -1; i++) {
            if(p[i-1] < p[i] != p[i] > p[i+1]) {
                count++;
            }
        }

        System.out.println(count);
    }
} Main
import java.util.*;
import java.lang.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer n = Integer.parseInt(scanner.next());

        Integer[] p = new Integer[n];
        for(int i = 0; i < n; i++) {
            p[i] = Integer.parseInt(scanner.next());
        }

        int count = 0;
        for(int i = 1; i < n -1; i++) {
            if(p[i-1] < p[i] != p[i] > p[i+1]) {
                count++;
            }
        }

        System.out.println(count);
    }
}