import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {

    private void solve() {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i <= n-2; 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.print(ans);
    }

    // Main
    public static void main(String[] args) {
        new Main().solve();
    }
}
 import java.util.ArrayList; ArrayList java.util import java.util.List; List java.util import java.util.Scanner; Scanner java.util public class Main {

    private void solve() {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i <= n-2; 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.print(ans);
    }

    // Main
    public static void main(String[] args) {
        new Main().solve();
    }
} Main private void solve() {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i <= n-2; 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.print(ans);
    } solve {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i <= n-2; 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.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 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 int ans = 0; ans 0 for (int i = 1; i <= n-2; 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-2 i n-2 n 2 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.print(ans) System.out.print System.out System System.out ans // Main
    public static void main(String[] args) {
        new Main().solve();
    } main {
        new Main().solve();
    } new Main().solve() new Main().solve new Main() String[] args args public class Main {

    private void solve() {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i <= n-2; 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.print(ans);
    }

    // Main
    public static void main(String[] args) {
        new Main().solve();
    }
} public class Main {

    private void solve() {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i <= n-2; 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.print(ans);
    }

    // Main
    public static void main(String[] args) {
        new Main().solve();
    }
} Main
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {

    private void solve() {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] p = new int[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }

        int ans = 0;
        for (int i = 1; i <= n-2; 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.print(ans);
    }

    // Main
    public static void main(String[] args) {
        new Main().solve();
    }
}

