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.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.StringTokenizer;

public class SuperTree {
	public static BufferedReader sc = new BufferedReader(new InputStreamReader(System.in));
	public static StringTokenizer st;
	public static PrintWriter pw = new PrintWriter(System.out);
	final static boolean debugmode = true;
	public static int k = 7; // for 10^9 + k mods.
	public static long STMOD = 1000000000 + k; // 10^9 + k
	public static void main(String[] args) throws IOException{
		int i = getInt();
		if(i <= 5){
			submit(-1,false);
		}
		else{
			String p = "1 2\n1 3\n1 4\n2 5\n 2 6";
			submit(p,false);
			for(int r = 7;r <= i;r++){
				submit(r+ " 2",false);
			}
		}
		for(int q = 1;q<i;q++){
			submit((q+1)+" 1",false);
		}
		submit();
	}
	public static void setInputFile(String fn) throws IOException{
		sc = new BufferedReader(new FileReader(fn));
	}
	public static void setOutputFile(String fn) throws IOException{
		 pw = new PrintWriter(new BufferedWriter(new FileWriter(fn)));
	}
	public static int GCD(int a, int b) {
		   if (b==0) return a;
		   return GCD(b,a%b);
	}
	public static double log(int k, int v){
		return Math.log(k)/Math.log(v);
	}
	
	public static long longpower(int a,int b){
		long[] vals = new long[(int) (log(b,2)+2)];
		vals[0] = a;
		vals[1] = a*a;
		for(int i = 1;i<vals.length;i++){
			vals[i] = vals[i-1]*vals[i-1];
		}
		long ans = 1;
		int cindex = 0;
		while(b != 0){
			if (b % 2 == 1){
				ans *= vals[cindex];
			}
			cindex += 1;
			b /= 2;
		}
		return ans;
		
		
	}
	
	public static void debug(String toPrint){
		if(!debugmode) {return;}
		pw.println("[DEBUG]: "+toPrint);
	}
	public static void  submit(int[] k,boolean close){
		pw.println(Arrays.toString(k));
		if(close){
			pw.close();
		}
	}
	public static void submit(int p,boolean close){
		pw.println(Integer.toString(p));
		if(close){
			pw.close();
		}
	}
	public static void submit(String k,boolean close){
		pw.println(k);
		if(close){
			pw.close();
		}
	}
	public static void submit(double u,boolean close){
		pw.println(Double.toString(u));
		if(close){
			pw.close();
		}
	}
	public static void submit(long lng,boolean close){
		pw.println(Long.toString(lng));
		if(close){
			pw.close();
		}
		
	}
	public static void submit(){
		pw.close();
	}
	public static int getInt() throws IOException{
		if (st != null && st.hasMoreTokens()){
			return Integer.parseInt(st.nextToken());
		}
		st = new StringTokenizer(sc.readLine());
		return Integer.parseInt(st.nextToken());
	}
	public static long getLong() throws IOException{
		if (st != null && st.hasMoreTokens()){
			return Long.parseLong(st.nextToken());
		}
		st = new StringTokenizer(sc.readLine());
		return Long.parseLong(st.nextToken());
	}
	public static double getDouble()throws IOException{
		if (st != null && st.hasMoreTokens()){
			return Double.parseDouble(st.nextToken());
		}
		st = new StringTokenizer(sc.readLine());
		return Double.parseDouble(st.nextToken());
	}
	public static String getString()throws IOException{
		if(st != null && st.hasMoreTokens()){
			return st.nextToken();
		}
		st = new StringTokenizer(sc.readLine());
		return st.nextToken();
	}
	public static String getLine() throws IOException{
		return sc.readLine();
	}
	public static int[][] readMatrix(int lines,int cols) throws IOException{
		int[][] matrr = new int[lines][cols];
		for (int i = 0;i < lines;i++){
			for(int j = 0;j < cols;j++){
				matrr[i][j] = getInt();
			}
		}
		return matrr;
	}
	public static int[] readArray(int lines) throws IOException{
		int[] ar = new int[lines];		
		for (int i = 0;i<lines;i++) ar[i] =getInt();
		return ar;
	}
	
}