Problem: Mahmoud was trying to solve the vertex cover problem on trees. The problem statement is:

Given an undirected tree consisting of n nodes, find the minimum number of vertices that cover all the edges. Formally, we need to find a set of vertices such that for each edge (u, v) that belongs to the tree, either u is in the set, or v is in the set, or both are in the set. Mahmoud has found the following algorithm:

  * Root the tree at node 1. 
  * Count the number of nodes at an even depth. Let it be evenCnt. 
  * Count the number of nodes at an odd depth. Let it be oddCnt. 
  * The answer is the minimum between evenCnt and oddCnt. 



The depth of a node in a tree is the number of edges in the shortest path between this node and the root. The depth of the root is 0.

Ehab told Mahmoud that this algorithm is wrong, but he didn't believe because he had tested his algorithm against many trees and it worked, so Ehab asked you to find 2 trees consisting of n nodes. The algorithm should find an incorrect answer for the first tree and a correct answer for the second one.

Input

The only line contains an integer n (2 ≤ n ≤ 105), the number of nodes in the desired trees.

Output

The output should consist of 2 independent sections, each containing a tree. The algorithm should find an incorrect answer for the tree in the first section and a correct answer for the tree in the second. If a tree doesn't exist for some section, output "-1" (without quotes) for that section only.

If the answer for a section exists, it should contain n - 1 lines, each containing 2 space-separated integers u and v (1 ≤ u, v ≤ n), which means that there's an undirected edge between node u and node v. If the given graph isn't a tree or it doesn't follow the format, you'll receive wrong answer verdict.

If there are multiple answers, you can print any of them.

Examples

Input

2


Output

-1
1 2


Input

8


Output

1 2
1 3
2 4
2 5
3 6
4 7
4 8
1 2
1 3
2 4
2 5
2 6
3 7
6 8

Note

In the first sample, there is only 1 tree with 2 nodes (node 1 connected to node 2). The algorithm will produce a correct answer in it so we printed  - 1 in the first section, but notice that we printed this tree in the second section.

In the second sample:

In the first tree, the algorithm will find an answer with 4 nodes, while there exists an answer with 3 nodes like this: <image> In the second tree, the algorithm will find an answer with 3 nodes which is correct: <image>

Solution (in JAVA):

Solution:
import java.io.*;

public class CTreeCover {

  private static final String REGEX = " ";
  private static final Boolean DEBUG = false;
  private static final String FILE_NAME = "input.txt";


  public static void main(String[] args) throws IOException {
    if (DEBUG) {
      generate();
    }
    Solver solver = new Solver();
    solver.readData();
    solver.solve();
    solver.print();
  }

  private static void generate() throws IOException {
//    FileWriter writer = new FileWriter("input.txt");
//    writer.close();
  }

  private static class Solver {
    private StringBuilder myStringBuilder = new StringBuilder();
    int n;

    void readData() throws IOException {
      Scanner scanner = new Scanner();
      n = scanner.nextInt();
      scanner.close();
    }

    void solve() {
      printFirstPart();
      printSecondPart();
    }

    private void printFirstPart() {
      if (n <= 5) {
        out("-1\n");
      } else {
        out("1 2\n");
        out("2 3\n");
        out("2 4\n");
        for (int i = 5; i <= n; i++) {
          out("1 ");
          out(i);
          newLine();
        }
      }
    }

    void printSecondPart() {
      for (int i = 1; i <= n - 1; i++) {
        out(i);
        out(' ');
        out(i + 1);
        newLine();
      }
    }

    void print() {
      System.out.println(myStringBuilder);
    }


    void out(Object object) {
      myStringBuilder.append(object);
    }

    void out(String string) {
      myStringBuilder.append(string);
    }

    public void out(boolean b) {
      myStringBuilder.append(b);
    }

    public void out(char c) {
      myStringBuilder.append(c);
    }

    public void out(int i) {
      myStringBuilder.append(i);
    }

    public void out(long lng) {
      myStringBuilder.append(lng);
    }

    public void out(float f) {
      myStringBuilder.append(f);
    }

    public void out(double d) {
      myStringBuilder.append(d);
    }

    public void newLine() {
      myStringBuilder.append("\n");
    }

    @SuppressWarnings("SameParameterValue")
    int[] splitInteger(String string, int n) {
      final String[] split = string.split(REGEX, n);
      int[] result = new int[split.length];
      for (int i = 0; i < n; ++i) {
        result[i] = Integer.parseInt(split[i]);
      }
      return result;
    }

    public int[] splitInteger(String string) {
      return splitInteger(string, 0);
    }


    @SuppressWarnings("SameParameterValue")
    long[] splitLong(String string, int n) {
      final String[] split = string.split(REGEX, n);
      long[] result = new long[split.length];
      for (int i = 0; i < n; ++i) {
        result[i] = Long.parseLong(split[i]);
      }
      return result;
    }

    public long[] splitLong(String string) {
      return splitLong(string, 0);
    }

    @SuppressWarnings("SameParameterValue")
    double[] splitDouble(String string, int n) {
      final String[] split = string.split(REGEX, n);
      double[] result = new double[split.length];
      for (int i = 0; i < n; ++i) {
        result[i] = Double.parseDouble(split[i]);
      }
      return result;
    }

    public double[] splitDouble(String string) {
      return splitDouble(string, 0);
    }

    @SuppressWarnings("SameParameterValue")
    String[] splitString(String string, int n) {
      return string.split(REGEX, n);
    }

    public int max(int a, int b) {
      return Math.max(a, b);
    }

    public int max(int[] arr) {
      int max = Integer.MIN_VALUE;
      for (int x : arr) {
        max = max(max, x);
      }
      return max;
    }

    public long max(long a, long b) {
      return Math.max(a, b);
    }

    public int min(int a, int b) {
      return Math.min(a, b);
    }

    public long min(long a, long b) {
      return Math.min(a, b);
    }

    public double max(double a, double b) {
      return Math.max(a, b);
    }

    public double min(double a, double b) {
      return Math.min(a, b);
    }

    private final static int MOD = 1000000009;

    int multMod(int a, int b) {
      return ((a % MOD) * (b % MOD)) % MOD;
    }

    int sumMod(int a, int b) {
      return ((a % MOD) + (b % MOD)) % MOD;
    }

    long multMod(long a, long b) {
      return ((a % MOD) * (b % MOD)) % MOD;
    }

    long sumMod(long a, long b) {
      return ((a % MOD) + (b % MOD)) % MOD;
    }

    int sum(int[] arr) {
      int sum = 0;
      for (int i = 0; i < arr.length; i++) {
        sum += arr[i];
      }
      return sum;
    }

    long sum(long[] arr) {
      long sum = 0;
      for (int i = 0; i < arr.length; i++) {
        sum += arr[i];
      }
      return sum;
    }

    private class Scanner {
      private int currentIndex = 0;
      private String[] objects;
      private final BufferedReader myReader;
      private Computable<Character> charComputer;
      private Computable<Double> doubleComputer;
      private Computable<Integer> intComputer;
      private Computable<Long> longComputer;

      Scanner() throws FileNotFoundException {
        InputStream in = DEBUG ? new FileInputStream(FILE_NAME) : System.in;
        myReader = new BufferedReader(new InputStreamReader(in));
        charComputer = () -> objects[currentIndex].charAt(0);
        doubleComputer = () -> Double.parseDouble(objects[currentIndex]);
        intComputer = () -> Integer.parseInt(objects[currentIndex]);
        longComputer = () -> Long.parseLong(objects[currentIndex]);
      }

      String nextLine() throws IOException {
        objects = null;
        currentIndex = 0;
        return myReader.readLine();
      }

      int nextInt() throws IOException {
        return next(intComputer);
      }

      int[] nextIntArray(int n) throws IOException {
        return splitInteger(nextLine(), n);
      }

      long[] nextLongArray(int n) throws IOException {
        return splitLong(nextLine(), n);
      }

      long nextLong() throws IOException {
        return next(longComputer);

      }

      double nextDouble() throws IOException {
        return next(doubleComputer);

      }

      char nextChar() throws IOException {
        return next(charComputer);
      }

      <T> T next(Computable<T> computer) throws IOException {
        T result;
        if (objects == null || currentIndex >= objects.length) {
          String s = myReader.readLine();
          objects = s.split(" ");
          currentIndex = 0;
        }
        result = computer.compute();
        currentIndex++;
        return result;
      }

      public void close() throws IOException {
        myReader.close();
      }

    }

    interface Computable<T> {
      T compute();
    }

  }

}