import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            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++) {
                int min = Math.min(p[i - 1], p[i + 1]);
                int max = Math.max(p[i - 1], p[i + 1]);
                if (min < p[i] && p[i] < max)
                    ans++;
            }
            out.print(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

    }
}
 import java.io.OutputStream; OutputStream java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.StringTokenizer; StringTokenizer java.util import java.io.IOException; IOException java.io import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io import java.io.InputStream; InputStream java.io public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            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++) {
                int min = Math.min(p[i - 1], p[i + 1]);
                int max = Math.max(p[i - 1], p[i + 1]);
                if (min < p[i] && p[i] < max)
                    ans++;
            }
            out.print(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

    }
} Main public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    } InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out InputReader in = new InputReader(inputStream); in new InputReader(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) TaskB solver = new TaskB(); solver new TaskB() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            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++) {
                int min = Math.min(p[i - 1], p[i + 1]);
                int max = Math.max(p[i - 1], p[i + 1]);
                if (min < p[i] && p[i] < max)
                    ans++;
            }
            out.print(ans);
        }

    } TaskB public void solve(int testNumber, InputReader in, PrintWriter out) {
            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++) {
                int min = Math.min(p[i - 1], p[i + 1]);
                int max = Math.max(p[i - 1], p[i + 1]);
                if (min < p[i] && p[i] < max)
                    ans++;
            }
            out.print(ans);
        } solve {
            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++) {
                int min = Math.min(p[i - 1], p[i + 1]);
                int max = Math.max(p[i - 1], p[i + 1]);
                if (min < p[i] && p[i] < max)
                    ans++;
            }
            out.print(ans);
        } 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] p i in.nextInt() in.nextInt in int ans = 0; ans 0 for (int i = 1; i < n - 1; i++) {
                int min = Math.min(p[i - 1], p[i + 1]);
                int max = Math.max(p[i - 1], p[i + 1]);
                if (min < p[i] && p[i] < max)
                    ans++;
            } int i = 1; int i = 1; i 1 i < n - 1 i n - 1 n 1 i++ i++ i {
                int min = Math.min(p[i - 1], p[i + 1]);
                int max = Math.max(p[i - 1], p[i + 1]);
                if (min < p[i] && p[i] < max)
                    ans++;
            } {
                int min = Math.min(p[i - 1], p[i + 1]);
                int max = Math.max(p[i - 1], p[i + 1]);
                if (min < p[i] && p[i] < max)
                    ans++;
            } int min = Math.min(p[i - 1], p[i + 1]); min Math.min(p[i - 1], p[i + 1]) Math.min Math p[i - 1] p i - 1 i 1 p[i + 1] p i + 1 i 1 int max = Math.max(p[i - 1], p[i + 1]); max Math.max(p[i - 1], p[i + 1]) Math.max Math p[i - 1] p i - 1 i 1 p[i + 1] p i + 1 i 1 if (min < p[i] && p[i] < max)
                    ans++; min < p[i] && p[i] < max min < p[i] min p[i] p i p[i] < max p[i] p i max ans++ ans out.print(ans) out.print out ans int testNumber testNumber InputReader in in PrintWriter out out static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

    } InputReader public BufferedReader reader; reader public StringTokenizer tokenizer; tokenizer public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        } InputReader {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        } reader = new BufferedReader(new InputStreamReader(stream), 32768) reader new BufferedReader(new InputStreamReader(stream), 32768) tokenizer = null tokenizer null InputStream stream stream public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } next {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        } while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            } try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } catch (IOException e) {
                    throw new RuntimeException(e);
                } IOException e {
                    throw new RuntimeException(e);
                } throw new RuntimeException(e); new RuntimeException(e) {
                    tokenizer = new StringTokenizer(reader.readLine());
                } tokenizer = new StringTokenizer(reader.readLine()) tokenizer new StringTokenizer(reader.readLine()) return tokenizer.nextToken(); tokenizer.nextToken() tokenizer.nextToken tokenizer public int nextInt() {
            return Integer.parseInt(next());
        } nextInt {
            return Integer.parseInt(next());
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            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++) {
                int min = Math.min(p[i - 1], p[i + 1]);
                int max = Math.max(p[i - 1], p[i + 1]);
                if (min < p[i] && p[i] < max)
                    ans++;
            }
            out.print(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

    }
} public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            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++) {
                int min = Math.min(p[i - 1], p[i + 1]);
                int max = Math.max(p[i - 1], p[i + 1]);
                if (min < p[i] && p[i] < max)
                    ans++;
            }
            out.print(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            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++) {
                int min = Math.min(p[i - 1], p[i + 1]);
                int max = Math.max(p[i - 1], p[i + 1]);
                if (min < p[i] && p[i] < max)
                    ans++;
            }
            out.print(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

    }
}

