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.*;
import java.util.*;

public class CODEFORCES
{
	@SuppressWarnings("rawtypes")
	static InputReader in;
	static PrintWriter out;

	static void solve()
	{
		int n = in.ni();
		if (n < 6)
			out.println("-1");
		else
		{
			out.println("1 2");
			for (int i = 3; i <= n; i++)
			{
				if (i % 2 == 0)
					out.println(i + " 1");
				else
					out.println(i + " 2");
			}
		}
		for (int i = 1; i < n; i++)
			out.println(i + " " + (i + 1));
	}

	static int[][] graph(int from[], int to[], int n)
	{
		int g[][] = new int[n][];
		int cnt[] = new int[n];
		for (int i = 0; i < from.length; i++)
		{
			cnt[from[i]]++;
			cnt[to[i]]++;
		}
		for (int i = 0; i < n; i++)
			g[i] = new int[cnt[i]];
		Arrays.fill(cnt, 0);
		for (int i = 0; i < from.length; i++)
		{
			g[from[i]][cnt[from[i]]++] = to[i];
			g[to[i]][cnt[to[i]]++] = from[i];
		}
		return g;
	}

	@SuppressWarnings("rawtypes")
	static void soln()
	{
		in = new InputReader(System.in);
		out = new PrintWriter(System.out);
		solve();
		out.flush();
	}

	static void debug(Object... o)
	{
		System.out.println(Arrays.deepToString(o));
	}

	public static void main(String[] args)
	{
		new Thread(null, new Runnable()
		{
			public void run()
			{
				try
				{
					soln();
				} catch (Exception e)
				{
					e.printStackTrace();
				}
			}
		}, "1", 1 << 26).start();
	}

	// To Get Input
	// Some Buffer Methods
	static class InputReader<SpaceCharFilter>
	{

		private final InputStream stream;
		private final byte[] buf = new byte[8192];
		private int curChar, snumChars;
		private SpaceCharFilter filter;

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

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

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

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

		public int[] nextIntArray(int n)
		{
			int a[] = new int[n];
			for (int i = 0; i < n; i++)
			{
				a[i] = ni();
			}
			return a;
		}

		public long[] nextLongArray(int n)
		{
			long a[] = new long[n];
			for (int i = 0; i < n; i++)
			{
				a[i] = nl();
			}
			return a;
		}

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

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

		public boolean isSpaceChar(int c)
		{
			if (filter != null)
				return filter.isSpaceChar(c);
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}

		private boolean isEndOfLine(int c)
		{
			return c == '\n' || c == '\r' || c == -1;
		}

		public interface SpaceCharFilter
		{
			public boolean isSpaceChar(int ch);
		}

	}
}