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.math.*;
			        		    import java.util.*;
		import java.util.regex.Pattern;
		
		import javafx.scene.shape.Line;
			    	     
			        		    public class Main{
			        		  	private static InputStream stream;
			        		    	private static byte[] buf = new byte[1024];
			        		    	private static int curChar;
			        		    	private static int numChars;
			        		    	private static SpaceCharFilter filter;
			        		    	private static PrintWriter pw;
			        		    	private static long count = 0,mod=(long)1e9+7;
			        		    //	private static TreeSet<Integer> ts=new TreeSet[200000];
			public final static int INF = (int) 1E9;
			
			public static void main(String args[]) {
		    	
				InputReader(System.in);
				pw = new PrintWriter(System.out); 
			    new Thread(null ,new Runnable(){
			       public void run(){
			           try{
			        		
			               test();
		
			               pw.close();
			           } 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();
			    		//pw.println();
			    		//sb.append("\n");
			    	}
			    	//pw.println(sb);
			    }
			    
			    public static long pow(long n, long p,long mod) {
					if(p==0)
						return 1;
					if(p==1)
						return n%mod;
					if(p%2==0){
						long temp=pow(n, p/2,mod);
					return (temp*temp)%mod;
					}else{
						 	long temp=pow(n,p/2,mod);
						 	temp=(temp*temp)%mod;
						 	return(temp*n)%mod;
						 	
					}
				}
			    public static long pow(long n, long p) {
					if(p==0)
						return 1;
					if(p==1)
						return n;
					if(p%2==0){
						long temp=pow(n, p/2);
					return (temp*temp);
					}else{
						 	long temp=pow(n,p/2);
						 	temp=(temp*temp);
						 	return(temp*n);
						 	
					}
				}
			    public static void Merge(long a[],int p,int r){
			        if(p<r){
			            int q = (p+r)/2;
			            Merge(a,p,q);
			            Merge(a,q+1,r);
			            Merge_Array(a,p,q,r);
			        }
			    }
			    public static void Merge_Array(long a[],int p,int q,int r){
			       long b[] = new long[q-p+1];
			        long c[] = new long[r-q];
			        for(int i=0;i<b.length;i++)
			            b[i] = a[p+i];
			        for(int i=0;i<c.length;i++)
			            c[i] = a[q+i+1];
			        int i = 0,j = 0;
			        for(int k=p;k<=r;k++){
			            if(i==b.length){
			                a[k] = c[j];
			                j++;
			            }
			            else if(j==c.length){
			                a[k] = b[i];
			                i++;
			            }
			            else if(b[i]<c[j]){
			                a[k] = b[i];
			                i++;
			            }
			            else{
			                a[k] = c[j];
			                j++;
			            }
			        }
			    }
			    
			  
				public static long gcd(long x, long y) {
					if (x == 0)
						return y;
					else
						return gcd( y % x,x);
				}	
				
				public static boolean isPrime(int n) {
					if (n <= 1)
						return false;
					if (n <= 3)
						return true;
			 
					if (n % 2 == 0 || n % 3 == 0)
						return false;
			 
					for (int i = 5; i * i <= n; i = i + 6)
						if (n % i == 0 || n % (i + 2) == 0)
							return false;
			 
					return true;
				}
				
			        static LinkedList<Integer> adj[],adj2[];
			        static boolean Visited[];
			        static HashSet<Integer> exc;
			        static long oddsum[]=new long[1000001];
			        static long co=0;
			        static int indeg[],outdeg[];
	  		      
			    
			    	private static void buildgraph(int n){
			    		adj=new LinkedList[n+1];
			    		adj2=new LinkedList[n+1];
			    		Visited=new boolean[n+1];
			    		levl=new int[n+1];
			    		indeg=new int[n+1];
			    		outdeg=new int[n+1];
			    		for(int i=0;i<=n;i++){
			    			adj[i]=new LinkedList<Integer>();
			    			adj2[i]=new LinkedList<Integer>();
			    		}
			
			
			    	}
			      
			       
			        static int[] levl;
			        static int[] eat;
			        static int n,m;
			        static int price[];
			        //ind frog crab
			    
			        
			        static long d,x,y;
					static long modInverse(long A, long M)
					{
					extendedEuclid(A,M);
					return (x%M+M)%M;    //x may be negative
					}
					static void extendedEuclid(long A, long B) {
					if(B == 0) {
					d = A;
					x = 1;
					y = 0;
					}
					else {
					extendedEuclid(B, A%B);
					long temp = x;
					x = y;
					y = temp - (A/B)*y;
					}
					}
			        static double distance(int x1,int y1,int x2,int y2){
			        	return Math.sqrt((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2));
			        }
			        static double area(int x1, int y1, int x2, int y2, int x3, int y3)
			        {
			           return Math.abs((x1*(y2-y3) + x2*(y3-y1)+ x3*(y1-y2))/2.0);
			        }
			        static boolean isInside(int x1, int y1, int x2, int y2, int x3, int y3, int x, int y)
			        {   
			           double A = area (x1, y1, x2, y2, x3, y3);
			         
			           double A1 = area (x, y, x2, y2, x3, y3);
			         
			           double A2 = area (x1, y1, x, y, x3, y3);
			         
			           double A3 = area (x1, y1, x2, y2, x, y);
			           
			          return (A == A1 + A2 + A3);
			        }
			      
					static int col[];
			    public static boolean isVowel(char c){
			    	if(c=='a' || c=='e'||c=='i' || c=='o' || c=='u')
			    		return true;
			    	return false;
			    }
			static long arr[], lazy[],ans[];
			static int c[],nodes[];
			static int dp[][];
			static long a[][];
			
			private static boolean isPrim(long n,int p){
				for (long i = 2; i * i <= n; i++) {
			        if (n % i == 0 && i <= p) return false;
			    }
			    return true;
			}
			//price - starting index of string with given hash
			//rating-count of number of time of a hash
			static ArrayList<String> all_perm;
			static boolean[][] visited1;
			static  boolean won;
			static boolean containsCycle;
			static ArrayList<Integer> anss;
			private static int size = 0;
		public static void solve() throws IOException{
			HashSet<Integer> prime = new HashSet<Integer>();
			for(int i=2;i<=1;i++){
				if(isPrime(i))
					prime.add(i);
			}
			int n=nextInt();
			if(n==6 || n==7){
				pw.println("1 2");
				pw.println("1 3");
				pw.println("1 4");
				pw.println("2 5");
				pw.println("2 6");
				if(n==7){
					pw.println("2 7");
				}
			}
			else if(n<=5){
				pw.println(-1);
				
				
			}else{
				pw.println("1 2");
				pw.println("1 3");
				pw.println("2 4");
				pw.println("2 5");
				pw.println("3 6");
				pw.println("4 7");
				pw.println("4 8");
				for(int i=9;i<=n;i++){
					pw.println("4 "+i);
				}
				
				
			}
			//Correct answer
			for(int i=1;i<n;i++){
				pw.println(1+" "+(i+1));
			}
			
			
		}
			private static int mySoln(int n,int a,int b){
				int tempa=Math.min(a, b);
				int tempb=Math.max(a, b);
				ArrayList<Integer> list = new ArrayList<Integer>();
				for(int i=1;i<=n;i++){
					list.add(i);
				}
				
				int round=1;
				while(true){
					ArrayList<Integer> temp = new ArrayList<Integer>();
					
					for(int i=0;i<list.size();i+=2){
						if(list.get(i)==tempa && list.get(i+1)==tempb){
							
							return round;
						}
						if(list.get(i)==tempa ||  list.get(i)==tempb){
							temp.add(list.get(i));
						}else if(list.get(i+1)==tempa || list.get(i+1)==tempb){
							temp.add(list.get(i+1));
						}else{
							temp.add(list.get(i));
						}
					}
					
					list.clear();
					for(int i:temp){
						list.add(i);
					}
				
					round++;
				
					
				}
			}
			private static int othersoln(int n,int a,int b){
			for(int i=16;i>=0;i--){
				if(BB(a,i) ^ BB(b,i)){
					int m=i+1;
					
						return m;
								
			}
			}
			return 0;
			
			}
			private static boolean BB(int n,int i){
				return (n & (1<<i)) >0;
			}
					private static boolean check(int x,int y,int n,int m){
				if(x>=0 && x<n && y>=0 && y<m)
					return true;
				return false;
			}
					
					
					
					private static void dfs(int curr,int par){
				Visited[curr]=true;
				for(int i:adj[curr]){
					if(!Visited[i]){
						dfs(i,curr);
					}
				}
				dp[curr][nodes[curr]]++;
				for(int i=0;i<26;i++){
					dp[par][i]+=dp[curr][i];
				}
			}
		
			
			
			    private static boolean Check(int x,int y,int n){
					if(x>=0 && x<n && y>=0 && y<n)
						return true;
					return false;
				}
			    
			    public static String reverseString(String s) {
					StringBuilder sb = new StringBuilder(s);
					sb.reverse();
					return (sb.toString());
				}
			    
			  /*  
			   private static void BFS(int sou){
			    	Queue<Integer> q=new LinkedList<Integer>();
			    	q.add(sou);
			    	Visited[sou]=true;
			    	levl[sou]=0;
			    	while(!q.isEmpty()){
			    		int top=q.poll();
			    		
			    		for(int i:adj[top]){
			    			//pw.println(i+" "+top);
						if(!Visited[i])
						{
							
							q.add(i);
							levl[i]=levl[top]+1;
						}
						
						Visited[i]=true;
						
						}
					}
				}*/
				
			
			
			
			    		      
			    		   /* private static void kahn(int n){
			    		    	
			    		    	PriorityQueue<Integer> q=new PriorityQueue<Integer>();
			    				for(int i=1;i<=n;i++){
			    					if(indeg[i]==0){
			    						q.add(i);
			    					}
			    				}
			    				while(!q.isEmpty()){
			    					int top=q.poll();
			    					st.push(top);
			    					for(Node i:adj[top]){
			    						indeg[i.to]--;
			    						if(indeg[i.to]==0){
			    							q.add(i.to);
			    						}
			    					}
			    				}
			    		    }
			    		        
			    		        static int state=1;
			    		        static long no_exc=0,no_vert=0;
			    		      static Stack<Integer> st;
			    		      static HashSet<Integer> inset;
			    		     /*   private static void topo(int curr){
			    		        	
			    		        	Visited[curr]=true;
			    		        	inset.add(curr);
			    		        	for(int x:adj[curr]){
			    		        		if(adj[x].contains(curr) || inset.contains(x)){
			    		        			state=0;
			    		        			return;
			    		        		}
			    		        		if(state==0)
			    		        			return;
			    		        		
			    		        	}
			    		        	st.push(curr);
			    		        	
			    		        	inset.remove(curr);
			    		        }*/
			    		        static HashSet<Integer> hs;
			    		       
			    		     
			    		     	static boolean prime[];
								static int spf[];
								public static void sieve(int n){
									prime=new boolean[n+1];
									spf=new int[n+1];
									
									Arrays.fill(spf, 1);
									Arrays.fill(prime, true);
								prime[1]=false;
									spf[2]=2;
									
								for(int i=4;i<=n;i+=2){
									spf[i]=2;
								}
								for(int i=3;i<=n;i+=2){
									if(prime[i]){
										spf[i]=i;
										for(int j=2*i;j<=n;j+=i){
											
											prime[j]=false;
										if(spf[j]==1){
											spf[j]=i;
										}
										}
									}
								}
								
									
								}
			    		     	
			    		    	// To Get Input
			// Some Buffer Methods
			 
			    		     	public static void sort(long a[]){
			    		     		Merge(a, 0, a.length-1);
			    		     	}
			    		    	public static void InputReader(InputStream stream1) {
			    		    		stream = stream1;
			    		    	}
			 
			    		    	private static boolean isWhitespace(int c) {
			    		    		return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
			    		    	}
			 
			    		    	private static boolean isEndOfLine(int c) {
			    		    		return c == '\n' || c == '\r' || c == -1;
			    		    	}
			 
			    		    	private static 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++];
			    		    	}
			 
			    		    	private static 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 < '0' || c > '9')
						throw new InputMismatchException();
					res *= 10;
					res += c - '0';
			    		    			c = read();
			    		    		} while (!isSpaceChar(c));
			    		    		return res * sgn;
			    		    	}
			 
			    		    	private static 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;
			    		    	}
			 
			    		    	private static String nextToken() {
			    		    		int c = read();
			    		    		while (isSpaceChar(c))
			    		    			c = read();
			    		    		StringBuilder res = new StringBuilder();
			    		    		do {
			    		    			res.appendCodePoint(c);
			    		    			c = read();
			    		    		} while (!isSpaceChar(c));
			    		    		return res.toString();
			    		    	}
			 
			    		    	private static String nextLine() {
			    		    		int c = read();
			    		    		while (isSpaceChar(c))
			    		    			c = read();
			    		    		StringBuilder res = new StringBuilder();
			    		    		do {
			    		    			res.appendCodePoint(c);
			    		    			c = read();
			    		    		} while (!isEndOfLine(c));
			    		    		return res.toString();
			    		    	}
			 
			    		    	private static int[] nextIntArray(int n) {
			    		    		int[] arr = new int[n];
			    		    		for (int i = 0; i < n; i++) {
			    		    			arr[i] = nextInt();
			    		    		}
			    		    		return arr;
			    		    	}
			 
			    		    	private static long[][] next2dArray(int n, int m) {
			    		    		long[][] arr = new long[n][m];
			    		    		for (int i = 0; i < n; i++) {
			    		    			for (int j = 0; j < m; j++) {
			    		    				arr[i][j] = nextLong();
			    		    			}
			    		    		}
			    		    		return arr;
			    		    	}
			    		    	private static char[][] nextCharArray(int n,int m){
			    		    		char [][]c=new char[n][m];
			    		    		for(int i=0;i<n;i++){
			    		    			String s=nextLine();
			    		    			for(int j=0;j<s.length();j++){
			    		    				c[i][j]=s.charAt(j);
			    		    			}
			    		    		}
			    		    		return c;
			    		    	}
			 
			    		    	private static long[] nextLongArray(int n) {
			    		    		long[] arr = new long[n];
			    		    		for (int i = 0; i < n; i++) {
			    		    			arr[i] = nextLong();
			    		    		}
			    		    		return arr;
			    		    	}
			 
			    		    	private static void pArray(int[] arr) {
			    		    		for (int i = 0; i < arr.length; i++) {
			    		    			pw.print(arr[i] + " ");
			    		    		}
			    		    		pw.println();
			    		    		return;
			    		    	}
			 
			    		    	private static void pArray(long[] arr) {
			    		    		for (int i = 0; i < arr.length; i++) {
			    		    			pw.print(arr[i] + " ");
			    		    		}
			    		    		pw.println();
			    		    		return;
			    		    	}
			 
			    		    	private static void pArray(boolean[] arr) {
			    		    		for (int i = 0; i < arr.length; i++) {
			    		    			pw.print(arr[i] + " ");
			    		    		}
			    		    		pw.println();
			    		    		return;
			    		    	}
			 
			    		    	private static boolean isSpaceChar(int c) {
			    		    		if (filter != null)
			    		    			return filter.isSpaceChar(c);
			    		    		return isWhitespace(c);
			    		    	}
			 
			    		    	private interface SpaceCharFilter {
			    		    		public boolean isSpaceChar(int ch);
			    		    	}
			    		    	
			
			}
			    		    
			    		        class Node{
			    		    	int to;
			    		    	long dist;
			    		    	Node(int to,long dist){
			    		    		this.to=to;
			    		    		this.dist=dist;
			    		    	}
			    		    	
			    		    }
			    		        class Qu{
			    		    		long a0,a1,a2,a3;
			    		    		public Qu(long a0,long a1,long a2,long a3) {
			    		    			this.a0=a0;
			    		    			this.a1=a1;
			    		    			this.a2=a2;
			    		    			this.a3=a3;
			    		    		}
			    		    }
			    		
			class Dsu{
			private int rank[], parent[] ,n;
			long str[],si[],larg[];
			long max=0;
			int cnt=0;
			private static int[] parent1;
			Dsu(int size){
				this.n=size+1;
				rank=new int[n];
				cnt=n-1;
				//parent=new int[n];
			    		    		    		parent=new int[n];
			    		    		    		str=new long[n];
			    		    		    		si=new long[n];
			    		    		
			    		    		    		larg=new long[n];
			    		    		    		makeSet();
			    		    		
			    		    		    	}
			    		    		    	
			    		    		    	void makeSet(){
			    		    		    		for(int i=0;i<n;i++){
			    		    		    			parent[i]=i;
			    		    		    			si[i]=1;
			    		    		    		}
			    		    		    	}
			    		    		    	
			    		    		    	int find(int x){
			    		    		    		if(parent[x]!=x){
			    		    		    			
			    		    		    			parent[x]=find(parent[x]);
			    		    		    		}
			    		    		    		return parent[x];
			    		    		    	}
			    		    		    	
			    		    		    	void join(int ind,long val){
			    		    		    		if(str[ind]==0){
			    		    		    			str[ind]=val;
			    		    		    			larg[ind]=val;
			    		    		    			max=Math.max(max, str[ind]);
			    		    		    		}
			    		    		    		int prev_ind=(ind-1);
			    		    		    		int next_ind=(ind+1);
			    		    		    		if(prev_ind>0 && larg[prev_ind]!=0){
			    		    		    			union(prev_ind,ind);
			    		    		    		}
			    		    		    		if(next_ind<n && larg[next_ind]!=0){
			    		    		    			union(next_ind,ind);
			    		    		    		}
			    		    		    		
			    		    		    	}
			    		    		    
			    		    		    	
			    		    		    	boolean union(int x,int y){
			    		    		    		int xRoot=find(x);
			    		    		    		int yRoot=find(y);
			    		    		    
			    		    		    	
			    		    		    		if(xRoot==yRoot)
			    		    		    			return false;
			    		    		    		if(rank[xRoot]<rank[yRoot]){
			    		    		    		parent[xRoot]=yRoot;
			    		    		    		
			    		    		    		larg[yRoot]=Math.max(larg[xRoot], larg[yRoot]);
			    		    		    		
			    		    		    		si[yRoot]+=si[xRoot];
			    		    		    		str[yRoot]=larg[yRoot]*si[yRoot];
			    		    		    			max=Math.max(str[yRoot], max);
			    		    		    		}else if(rank[yRoot]<rank[xRoot]){
			    		    		    			parent[yRoot]=xRoot;
			     
			    		    		    			larg[xRoot]=Math.max(larg[xRoot], larg[yRoot]);
			        		    		    		
			        		    		    		si[xRoot]+=si[yRoot];
			        		    		    		str[xRoot]=larg[xRoot]*si[xRoot];
			    			    		    		max=Math.max(str[xRoot], max);
			    		    		    		}else{
			    		    		    			parent[yRoot]=xRoot;
			    		    		    			rank[xRoot]++;
			     
			    		    		    			larg[xRoot]=Math.max(larg[xRoot], larg[yRoot]);
			        		    		    		
			        		    		    		si[xRoot]+=si[yRoot];
			        		    		    		str[xRoot]=larg[xRoot]*si[xRoot];
			    			    		    		max=Math.max(str[xRoot], max);
			    		    		    		
			    		    		    		}
			    		    		    		cnt--;
			    		    		    		return true;
			    		    		    	}
			    	
			    		    		     
			    		    		    }
		class Pair1 implements Comparable<Pair1>{
				long price,rating;
				Pair1(long a,long b){
					this.price=a;
					this.rating=b;
				}
				@Override
				public int compareTo(Pair1 arg0) {
					
						return (int)(price-arg0.price);
					
				}
			
			
			}