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:
//pakage joney_000[let_me_start]
//
import java.util.*;
import java.lang.*;
import java.io.*;
import java.math.*;
/*
 * Author    : joney_000[let_me_start]
 * Algorithm : N/A
 * Platform  : N/A
 *
 */


/*    The Main Class                */
public class A{
 
  private InputStream inputStream ;
  private OutputStream outputStream ;
  private FastReader in ;
  private PrintWriter out ;
  /*
    Overhead [Additional Temporary Strorage] but provides memory reusibility for multiple test cases.
    Size Limit : 10^5 + 4 
  */
  private final int BUFFER = 50;
  private int    tempints[] = new int[BUFFER];
  private long   templongs[] = new long[BUFFER];
  private double tempdoubles[] = new double[BUFFER];
  private char   tempchars[] = new char[BUFFER];
  //private final long mod = 1000000000+7;
  private final int  INF  = Integer.MAX_VALUE / 10;
  private final long INF_L  = Long.MAX_VALUE / 10;

  public A(){}
  public A(boolean stdIO)throws FileNotFoundException{
    // stdIO = false;
    if(stdIO){
      inputStream = System.in;
      outputStream = System.out;
    }else{
      inputStream = new FileInputStream("output.txt");
      outputStream = new FileOutputStream("output1.txt");
    }
    in = new FastReader(inputStream);
    out = new PrintWriter(outputStream);

  }
  void run()throws Exception{
    int n = i();
    if(n == 2){
      out.write("-1\n1 2");
      return;
    }else if(n == 3){
      out.write("-1\n1 2\n1 3");
      return;
    }else if(n == 4){
      out.write("-1\n1 2\n1 3\n2 4");
      return;
    }else if(n == 5){
      out.write("-1\n1 2\n1 3\n2 4\n2 5");
      return;
    }else{
      out.write("1 2\n");
      int node = 2;
      for(int i = 1; i <= (n - 2)/2; i++){
        ++node;
        out.write("1 "+(node)+"\n");
        
      }
      for(int i = 1; i <= n - 2 - ((n - 2)/2); i++)out.write("2 "+(++node)+"\n");
      
      for(int i = 2; i <= n; i++)out.write(""+(i-1)+" "+i+"\n");
    }
    // out.write(""+ans+"\n");
  }// end run

  void clear(){
    
  }

  //****************************** Gerenal Utilities ***********************//

  void print_r(Object... o){
    out.write("\n"+Arrays.deepToString(o)+"\n");
    out.flush();
  }

  boolean isPrime(long n){
    if(n==1)return false;
    if(n<=3)return true;
    if(n%2==0)return false;
    for(int i=2 ;i <= Math.sqrt(n); i++){
      if(n%i==0)return false;
    }
    return true;
  }
  // sieve
  int[] primes(int n){       // for(int i=1;i<=arr.length-1;i++)out.write(""+arr[i]+" ");
    boolean arr[] = new boolean[n+1];
    Arrays.fill(arr,true);
    arr[1]=false;
    for(int i=2;i<=Math.sqrt(n);i++){
      if(!arr[i])continue;
      for(int j = 2*i ;j<=n;j+=i){
        arr[j]=false;
      }
    }
    LinkedList<Integer> ll = new LinkedList<Integer>();
    for(int i=1;i<=n;i++){  
      if(arr[i])ll.add(i);
    }
    n = ll.size();
    
    int primes[] = new int[n+1];
    for(int i=1;i<=n;i++){
      primes[i]=ll.removeFirst();
    }
    return primes;
  }

  long gcd(long a , long b){
    if(b==0)return a;
    return gcd(b , a%b);
  }

  long lcm(long a , long b){
    if(a==0||b==0)return 0;
    return (a*b)/gcd(a,b);
  }

  long mulmod(long a , long b ,long mod){
    if(a==0||b==0)return 0;
    if(b==1)return a;
    long ans = mulmod(a,b/2,mod);
    ans = (ans*2)% mod;
    if(b%2==1)ans = (a + ans)% mod;
    return ans;
  }
  
  long pow(long a , long b ,long mod){
    if(b==0)return 1;
    if(b==1)return a;
    long ans = pow(a,b/2,mod);
    ans = (ans * ans);
    if(ans >= mod )ans %= mod;

    if(b%2==1)ans = (a * ans);
    if(ans >= mod )ans %= mod;

    return ans;
  }
  // 20*20   nCr Pascal Table
  long[][] ncrTable(){
    long ncr[][] = new long[21][21];
    for(int i=0 ;i<=20 ;i++){ncr[i][0]=1;ncr[i][i]=1;}
      for(int j=0;j<=20 ;j++){
        for(int i=j+1;i<= 20 ;i++){
          ncr[i][j] = ncr[i-1][j]+ncr[i-1][j-1];
        }
      }
    return ncr;
  }
  //*******************************I/O******************************//  
  int i()throws Exception{
    //return Integer.parseInt(br.readLine().trim());
    return in.nextInt();
  }
  int[] is(int n)throws Exception{
  //int arr[] = new int[n+1];
    for(int i=1 ; i <= n ;i++)tempints[i] = in.nextInt();  
      return tempints;
  }
  long l()throws Exception{
    return in.nextLong();
  }
  long[] ls(int n)throws Exception{
    for(int i=1 ; i <= n ;i++)templongs[i] = in.nextLong();  
      return templongs;
  }

  double d()throws Exception{
    return in.nextDouble();
  }
  double[] ds(int n)throws Exception{
    for(int i=1 ; i <= n ;i++)tempdoubles[i] = in.nextDouble();  
      return tempdoubles;
  }
  char c()throws Exception{
    return in.nextCharacter();
  }
  char[] cs(int n)throws Exception{
    for(int i=1 ; i <= n ;i++)tempchars[i] = in.nextCharacter();  
      return tempchars;
  }
  String s()throws Exception{
    return in.nextLine();
  }
  BigInteger bi()throws Exception{
    return in.nextBigInteger();
  }
//***********************I/O ENDS ***********************//
//*********************** 0.3%f [precision]***********************//
/* roundoff upto 2 digits 
   double roundOff = Math.round(a * 100.0) / 100.0;
                    or
   System.out.printf("%.2f", val);
          
*/
/*
  print upto 2 digits after decimal
  val = ((long)(val * 100.0))/100.0;
  
*/    

    private void closeResources(){
     out.flush();
     out.close();
     return;
    }
    public static void main(String[] args) throws java.lang.Exception{
    //let_me_start Shinch Returns 


    /*  
        // Old Reader Writer
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter out=new BufferedWriter(new OutputStreamWriter(System.out));
    BufferedReader br=new BufferedReader(new FileReader("input.txt"));
        BufferedWriter out=new BufferedWriter(new FileWriter("output.txt"));
    */   
        A driver = new A(true);
        
        driver.run();

        driver.closeResources();
        return ;

      }  

    }

    class FastReader{

      private boolean finished = false;

      private InputStream stream;
      private byte[] buf = new byte[4 * 1024];
      private int curChar;
      private int numChars;
      private SpaceCharFilter filter;

      public FastReader(InputStream stream){
        this.stream = stream;
      }

      public int read(){
        if (numChars == -1){
          throw new InputMismatchException ();
        }
        if (curChar >= numChars){
          curChar = 0;
          try{
            numChars = stream.read (buf);
          } catch (IOException e){
            throw new InputMismatchException ();
          }
          if (numChars <= 0){
            return -1;
          }
        }
        return buf[curChar++];
      }

      public int peek(){
        if (numChars == -1){
          return -1;
        }
        if (curChar >= numChars){
          curChar = 0;
          try{
            numChars = stream.read (buf);
          } catch (IOException e){
            return -1;
          }
          if (numChars <= 0){
            return -1;
          }
        }
        return buf[curChar];
      }

      public int nextInt(){
        int c = read ();
        while (isSpaceChar (c))
          c = read ();
        int sgn = 1;
        if (c == '-'){
          sgn = -1;
          c = read ();
        }
        int res = 0;
        do{
          if(c==','){
            c = read();
          }
          if (c < '0' || c > '9'){
            throw new InputMismatchException ();
          }
          res *= 10;
          res += c - '0';
          c = read ();
        } while (!isSpaceChar (c));
        return res * sgn;
      }

      public long nextLong(){
        int c = read ();
        while (isSpaceChar (c))
          c = read ();
        int sgn = 1;
        if (c == '-'){
          sgn = -1;
          c = read ();
        }
        long res = 0;
        do{
          if (c < '0' || c > '9'){
            throw new InputMismatchException ();
          }
          res *= 10;
          res += c - '0';
          c = read ();
        } while (!isSpaceChar (c));
        return res * sgn;
      }

      public String nextString(){
        int c = read ();
        while (isSpaceChar (c))
          c = read ();
        StringBuilder res = new StringBuilder ();
        do{
          res.appendCodePoint (c);
          c = read ();
        } while (!isSpaceChar (c));
        return res.toString ();
      }

      public boolean isSpaceChar(int c){
        if (filter != null){
          return filter.isSpaceChar (c);
        }
        return isWhitespace (c);
      }

      public static boolean isWhitespace(int c){
        return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
      }

      private String readLine0(){
        StringBuilder buf = new StringBuilder ();
        int c = read ();
        while (c != '\n' && c != -1){
          if (c != '\r'){
            buf.appendCodePoint (c);
          }
          c = read ();
        }
        return buf.toString ();
      }

      public String nextLine(){
        String s = readLine0 ();
        while (s.trim ().length () == 0)
          s = readLine0 ();
        return s;
      }

      public String nextLine(boolean ignoreEmptyLines){
        if (ignoreEmptyLines){
          return nextLine ();
        }else{
          return readLine0 ();
        }
      }

      public BigInteger nextBigInteger(){
        try{
          return new BigInteger (nextString ());
        } catch (NumberFormatException e){
          throw new InputMismatchException ();
        }
      }

      public char nextCharacter(){
        int c = read ();
        while (isSpaceChar (c))
          c = read ();
        return (char) c;
      }

      public double nextDouble(){
        int c = read ();
        while (isSpaceChar (c))
          c = read ();
        int sgn = 1;
        if (c == '-'){
          sgn = -1;
          c = read ();
        }
        double res = 0;
        while (!isSpaceChar (c) && c != '.'){
          if (c == 'e' || c == 'E'){
            return res * Math.pow (10, nextInt ());
          }
          if (c < '0' || c > '9'){
            throw new InputMismatchException ();
          }
          res *= 10;
          res += c - '0';
          c = read ();
        }
        if (c == '.'){
          c = read ();
          double m = 1;
          while (!isSpaceChar (c)){
            if (c == 'e' || c == 'E'){
              return res * Math.pow (10, nextInt ());
            }
            if (c < '0' || c > '9'){
              throw new InputMismatchException ();
            }
            m /= 10;
            res += (c - '0') * m;
            c = read ();
          }
        }
        return res * sgn;
      }

      public boolean isExhausted(){
        int value;
        while (isSpaceChar (value = peek ()) && value != -1)
          read ();
        return value == -1;
      }

      public String next(){
        return nextString ();
      }

      public SpaceCharFilter getFilter(){
        return filter;
      }

      public void setFilter(SpaceCharFilter filter){
        this.filter = filter;
      }

      public interface SpaceCharFilter{
        public boolean isSpaceChar(int ch);
      }
    }
    /******************** Pair class ***********************/

  class Pair implements Comparable<Pair>{
     public int a;
     public int b;
          public int c;
     public Pair(){
      this.a = 0;
      this.b = 0;
    }
    public Pair(int a,int b, int c){
      this.a = a;
      this.b = b;
      this.c = c;
    }
    public int compareTo(Pair p){
      if(this.a==p.a){
       return this.b-p.b;  
     }
     return p.a-this.a; 
   }
   public String toString(){
    return "a="+this.a+" b="+this.b;
  }

}