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

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

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