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.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.InputMismatchException;
import java.util.StringTokenizer;
/*
 * 
 * daiict
 *
 * 
 * 
 */

public class pprac
{
	FastScanner in;
	PrintWriter out;

	static int countc = 0;
	static int minm = countc;

	static ArrayList[] adj;
	static ArrayList[] aadj;
	static int last;
	static int n;
	static int m;

	static int[] dp1;
	static int[] dp2;
	static int color[];
	static int visited[];
	static int[] arr;
	static long[] brr;
	static double ans;
	static int array[];
	static int start[];
	static int finish[];
	static int pref[];
	static int tree[];
	static int maxval = 32;

	static int ttt[];
	static int sum = 0;
	static String s;

	static int cc = 0;
	static long min = Long.MAX_VALUE;

	static ArrayList<Integer> segt[];

	// for dfs do not delete
	static int dir[][] =
	{
			{ 1, 0 },
			{ 0, 1 },
			{ 0, -1 },
			{ -1, 0 } };

	static int[] seg;
	static long count = 1;
	static long mod = (long) 1e9 + 7;

	static int parent[];
	static int size[];

	static int[] l;
	static int[] r;
	static int[] next;
	static int[] cnt;
	static int[] block;

	static int bblock = 1001;

	static HashSet<String> set;
	static HashSet<String> set2;

	static int low[];
	static int disc[];
	static int time;
	static int acn[];

	static HashMap<Long, Integer> map;

	static class Pair implements Comparable<Pair>
	{
		int x;
		int y;
		int i;

		Pair(int l, int m, int i)
		{

			this.x = l;
			this.y = m;
			this.i = i;

		}

		public int compareTo(Pair p)
		{

			if (this.x / bblock == p.x / bblock)
			{
				return (int) (this.y - p.y);
			}
			return (int) (this.x / bblock - p.x / bblock);
		}

		public String toString()
		{
			return x + " " + y;
		}

		public boolean equals(Object o)
		{
			if (o instanceof Pair)
			{
				Pair a = (Pair) o;

				return this.x == a.x;
			}

			return false;
		}

		public int hashCode()
		{
			return new Long(x).hashCode() * 31 + new Long(y).hashCode();
		}

	}

	public static int gcd(int a, int b)
	{
		if (b == 0)
			return a;
		return gcd(b, a % b);
	}

	void build(int n)
	{ // build the tree
		for (int i = n - 1; i > 0; --i)
			seg[i] = Math.min(seg[i << 1], seg[i << 1 | 1]);
	}

	public static void modify(int p, int val, int n)
	{ // set value at position
		// p
		for (seg[p += n] = val; p > 1; p >>= 1)
			seg[p >> 1] = Math.min(seg[p], seg[p ^ 1]);
	}

	int query(int l, int r, int n)
	{ // sum on interval [l, r)
		int res = Integer.MAX_VALUE;

		if (l > r)
		{
			return res;
		}

		for (l += n, r += n; l < r; l >>= 1, r >>= 1)
		{
			if ((l & 1) == 1)
				res = Math.min(res, seg[l++]);
			if ((r & 1) == 1)
				res = Math.min(res, seg[--r]);
		}
		return res;
	}

	// public static void update(int x,int val){
	// while(x<=maxval){
	// tree[x] += val;
	// x = (x&-x);
	// }
	// }

	public static int read(int idx)
	{
		int sum = 0;

		while (idx >= 0)
		{
			sum += tree[idx];
			idx -= (idx & (-idx));
		}

		return sum;
	}

	public static int find(int i)
	{
		if (parent[i] != i)
		{
			return find(parent[i]);
		}

		return i;
	}

	public static void union(int a, int b)
	{
		int x = find(a);
		int y = find(b);

		if (x != y)
		{
			if (size[x] > size[y])
			{
				size[x] += size[y];
				parent[y] = x;
			} else
			{
				size[y] += size[x];
				parent[x] = y;
			}
		}
	}

			/* static */ void solve() throws NumberFormatException, InputMismatchException, IOException
	{

		// Scanner in = new Scanner(System.in);

		int n = in.nextInt();

		if (n < 6)
		{
			out.println(-1);

			for (int i = 0; i < n - 1; i++)
			{
				out.println(1 + " " + (i + 2));
			}
		} else
		{

			out.println(1 + " " + 2);
			out.println(2 + " " + 3);
			out.println(2 + " " + 4);

			for (int i = 5; i <= n; i++)
			{
				out.println(1 + " " + i);
			}

			for (int i = 0; i < n - 1; i++)
			{
				out.println(1 + " " + (i + 2));
			}
		}

	}

	public static String reverse(String s)
	{

		String ans = "";

		for (int i = s.length() - 1; i >= 0; i--)
		{
			ans += s.charAt(i);
		}

		return ans;

	}

	public static long sum(long x)
	{
		return x < 10 ? x : x % 10 + sum(x / 10);
	}

	public static long gcd(long x, long y)
	{
		if (x == 0)
			return y;
		else
			return gcd(y % x, x);
	}

	static long inv(long x, long mod)
	{
		long r, y;
		for (r = 1, y = mod - 2; y != 0; x = x * x % mod, y >>= 1)
		{
			if ((y & 1) == 1)
				r = r * x % mod;

		}
		return r;
	}

	public static long pow(long x, long y, long n)
	{
		if (y == 0)
			return 1 % n;
		if (y % 2 == 0)
		{
			long z = pow(x, y / 2, n);
			return (z * z) % n;
		}
		return ((x % n) * pow(x, y - 1, n)) % n;
	}

	public static boolean isPrime(long a)
	{
		// Corner cases
		if (a <= 1)
			return false;
		if (a <= 3)
			return true;

		// This is checked so that we can skip
		// middle five numbers in below loop
		if (a % 2 == 0 || a % 3 == 0)
			return false;

		for (long i = 5; i * i <= a; i = i + 6)
			if (a % i == 0 || a % (i + 2) == 0)
				return false;

		return true;
	}

	void run() throws NumberFormatException, InputMismatchException, IOException
	{
		in = new FastScanner();
		out = new PrintWriter(System.out);

		solve();

		out.close();
	}

	class FastScanner
	{
		BufferedReader br;
		StringTokenizer st;

		public FastScanner()
		{
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next()
		{
			while (st == null || !st.hasMoreTokens())
			{
				try
				{
					st = new StringTokenizer(in.br.readLine());
				} catch (IOException e)
				{
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

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

		long nextLong()
		{
			return Long.parseLong(next());
		}

		double nextDouble()
		{
			return Double.parseDouble(next());
		}
	}

	public static void main(String[] args) throws NumberFormatException, InputMismatchException, IOException
	{
		// new Thread(null ,new Runnable(){
		// public void run(){
		// try{
		//
		// test();
		//
		// } catch(Exception e){
		// e.printStackTrace();
		// }
		// }
		// },"1",1<<26).start();
		// }
		// static StringBuilder sb;
		// public static void test() throws IOException{
		// sb=new StringBuilder();
		// int t=1;
		// while(t-->0){
		//
		// solve();
		//
		// }
		//

		new pprac().run();
	}

}

class Node
{
	int a;
	int b;

	public Node(int i, int j)
	{
		this.a = i;
		this.b = j;

	}

}

class MyComp implements Comparator<String>
{

	int c = 0;

	MyComp(int d)
	{
		c = d;
	}

	@Override
	public int compare(String a, String b)
	{

		// < == -1

		String arr[] = a.split(" ");
		String brr[] = b.split(" ");

		return arr[c].compareTo(brr[c]);

	}

}

class MyComp2 implements Comparator<Node>
{

	@Override
	public int compare(Node a, Node b)
	{

		// < == -1

		if (a.b > b.b)
		{
			return -1;
		} else
		{
			return 1;
		}

	}

}