Problem: A programming coach has n students to teach. We know that n is divisible by 3. Let's assume that all students are numbered from 1 to n, inclusive.

Before the university programming championship the coach wants to split all students into groups of three. For some pairs of students we know that they want to be on the same team. Besides, if the i-th student wants to be on the same team with the j-th one, then the j-th student wants to be on the same team with the i-th one. The coach wants the teams to show good results, so he wants the following condition to hold: if the i-th student wants to be on the same team with the j-th, then the i-th and the j-th students must be on the same team. Also, it is obvious that each student must be on exactly one team.

Help the coach and divide the teams the way he wants.

Input

The first line of the input contains integers n and m (3 ≤ n ≤ 48, <image>. Then follow m lines, each contains a pair of integers ai, bi (1 ≤ ai < bi ≤ n) — the pair ai, bi means that students with numbers ai and bi want to be on the same team.

It is guaranteed that n is divisible by 3. It is guaranteed that each pair ai, bi occurs in the input at most once.

Output

If the required division into teams doesn't exist, print number -1. Otherwise, print <image> lines. In each line print three integers xi, yi, zi (1 ≤ xi, yi, zi ≤ n) — the i-th team. 

If there are multiple answers, you are allowed to print any of them.

Examples

Input

3 0


Output

3 2 1 


Input

6 4
1 2
2 3
3 4
5 6


Output

-1


Input

3 3
1 2
2 3
1 3


Output

3 2 1 

Solution (in JAVA):

Solution:

	
	    /*
	     * Author- Priyam Vora
	     * BTech 2nd Year DAIICT
	     */
	     
	            
	    import java.io.*;
	    import java.math.*;
	    import java.util.*;
	    import javax.print.attribute.SetOfIntegerSyntax;
	     
	    public class Graph1 {
	    	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=1000000007;
	    	private static TreeSet<Integer>ts[]=new TreeSet[200000];
	    	private static HashSet hs=new HashSet();
	     
	    	public static void main(String args[]) throws Exception {
	    		InputReader(System.in);
	    		pw = new PrintWriter(System.out);
	    		//ans();
	    		soln();
	    		pw.close();
	    	}
	     
	    	public static long gcd(long x, long y) {
	    		if (x == 0)
	    			return y;
	    		else
	    			return gcd( y % x,x);
	    	}
	    	
	    	private static int BinarySearch(int a[], int low, int high, int target) {
	    		if (low > high)
	    			return -1;
	    		int mid = low + (high - low) / 2;
	    		if (a[mid] == target)
	    			return mid;
	    		if (a[mid] > target)
	    			high = mid - 1;
	    		if (a[mid] < target)
	    			low = mid + 1;
	    		return BinarySearch(a, low, high, target);
	    	}
	    	
	    	public static String reverseString(String s) {
	    		StringBuilder sb = new StringBuilder(s);
	    		sb.reverse();
	    		return (sb.toString());
	    	}
	    	
	    	public static long pow(long n, long p) {
	    		if(p==0)
	    			return 1;
	    		if(p==1)
	    			return n%mod;
	    		if(p%2==0){
	    			long temp=pow(n, p/2);
	    		return (temp*temp)%mod;
	    		}else{
	    			 	long temp=pow(n,p/2);
	    			 	temp=(temp*temp)%mod;
	    			 	return(temp*n)%mod;
	    			 	
	    		}
	    	}
	     
	    		
	     
	    	public static int[] radixSort(int[] f) {
	    		int[] to = new int[f.length];
	    		{
	    			int[] b = new int[65537];
	    			for (int i = 0; i < f.length; i++)
	    				b[1 + (f[i] & 0xffff)]++;
	    			for (int i = 1; i <= 65536; i++)
	    				b[i] += b[i - 1];
	    			for (int i = 0; i < f.length; i++)
	    				to[b[f[i] & 0xffff]++] = f[i];
	    			int[] d = f;
	    			f = to;
	    			to = d;
	    		}
	    		{
	    			int[] b = new int[65537];
	    			for (int i = 0; i < f.length; i++)
	    				b[1 + (f[i] >>> 16)]++;
	    			for (int i = 1; i <= 65536; i++)
	    				b[i] += b[i - 1];
	    			for (int i = 0; i < f.length; i++)
	    				to[b[f[i] >>> 16]++] = f[i];
	    			int[] d = f;
	    			f = to;
	    			to = d;
	    		}
	    		return f;
	    	}
	     
	    	public static int nextPowerOf2(final int a) {
	    		int b = 1;
	    		while (b < a) {
	    			b = b << 1;
	    		}
	    		return b;
	    	}
	     
	    	public static boolean PointInTriangle(int p1, int p2, int p3, int p4, int p5, int p6, int p7, int p8) {
	    		int s = p2 * p5 - p1 * p6 + (p6 - p2) * p7 + (p1 - p5) * p8;
	    		int t = p1 * p4 - p2 * p3 + (p2 - p4) * p7 + (p3 - p1) * p8;
	     
	    		if ((s < 0) != (t < 0))
	    			return false;
	     
	    		int A = -p4 * p5 + p2 * (p5 - p3) + p1 * (p4 - p6) + p3 * p6;
	    		if (A < 0.0) {
	    			s = -s;
	    			t = -t;
	    			A = -A;
	    		}
	    		return s > 0 && t > 0 && (s + t) <= A;
	    	}
	     
	    	public static float area(int x1, int y1, int x2, int y2, int x3, int y3) {
	    		return (float) Math.abs((x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2)) / 2.0);
	    	}
	     
	    	public static boolean isPrime(int n) {
	    		// Corner cases
	    		if (n <= 1)
	    			return false;
	    		if (n <= 3)
	    			return true;
	     
	    		// This is checked so that we can skip 
	    		// middle five numbers in below loop
	    		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;
	    	}
	     
	    	//merge Sort
	     
	    	static long sort(int a[])
	    	{  int n=a.length;
	    		int b[]=new int[n];	
	    		return mergeSort(a,b,0,n-1);}
	    	static long mergeSort(int a[],int b[],long left,long right)
	    	{ long c=0;if(left<right)
	    	 {   long mid=left+(right-left)/2;
	    		 c= mergeSort(a,b,left,mid);
	    		 c+=mergeSort(a,b,mid+1,right);
	    		 c+=merge(a,b,left,mid+1,right); }	
	    		return c;	 }
	    	static long merge(int a[],int  b[],long left,long mid,long right)
	    	{long c=0;int i=(int)left;int j=(int)mid; int k=(int)left;
	    	while(i<=(int)mid-1&&j<=(int)right)
	    	{ if(a[i]>a[j]) {b[k++]=a[i++]; }
	    	else	{ b[k++]=a[j++];c+=mid-i;}}
	    	while (i <= (int)mid - 1)   b[k++] = a[i++]; 
	    	while (j <= (int)right) b[k++] = a[j++];
	    	for (i=(int)left; i <= (int)right; i++) 
	    		a[i] = b[i];  return c;  }
	    	public static boolean isSubSequence(String large, String small, int largeLen, int smallLen) {
	    		//base cases
	    		if (largeLen == 0)
	    			return false;
	    		if (smallLen == 0)
	    			return true;
	    		// If last characters of two strings are matching
	    		if (large.charAt(largeLen - 1) == small.charAt(smallLen - 1))
	    			isSubSequence(large, small, largeLen - 1, smallLen - 1);
	    		// If last characters are not matching
	    		return isSubSequence(large, small, largeLen - 1, smallLen);
	    	}
	     
	    	// To Get Input
	    	// Some Buffer Methods
	     
	    	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 int[][] next2dArray(int n, int m) {
	    		int[][] arr = new int[n][m];
	    		for (int i = 0; i < n; i++) {
	    			for (int j = 0; j < m; j++) {
	    				arr[i][j] = nextInt();
	    			}
	    		}
	    		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);
	    	}
	     
	    	//----------------------------------------My Code------------------------------------------------//
	
	     
	    		
	    	private static void soln() {
	    int n=nextInt();
	    int m=nextInt();
	Graph g=new Graph(n);
	int freq[]=new int [n+1]; 
	if(m==0){
		for(int i=1;i<=n;i+=3){
			System.out.print(i+" "+(i+1)+" "+(i+2));
		System.out.println();
		
		}
		System.exit(0);
	}
	while(m-->0){
	    	int v=nextInt();
	    	int w=nextInt();
	    	g.addEdge(v, w);
	    	g.addEdge(w, v);
	   freq[v]++;
	   freq[w]++;
	    }
TreeSet<Integer> ss=new TreeSet();
for(int i=1;i<=n;i++){
	if(freq[i]==0)
		ss.add(i);
}
StringBuilder sb=new StringBuilder();
	    for(int i=1;i<=n;i++){
	    	long no=g.dfs(i);
	    	if(no%3==0){
	    		if(g.getEd()%3==0)
	    			sb.append(g.print_team()+"\n");
	    			
	    	}
	    	if(no==2){
	    		if(ss.size()!=0){
	    			sb.append(g.print_team());
	    			sb.append(ss.first()+"\n");
	    			ss.remove(ss.first());
	    		}else{
	    			System.out.println(-1);
	    			System.exit(0);
	    		}
	    	}
	    	if(no>3){
	    		System.out.println(-1);
	    		System.exit(0);
	    	}
	    	
	    }
	    while(!ss.isEmpty()){
	    	sb.append(ss.first()+" ");
	    	ss.remove(ss.first());
	    	sb.append(ss.first()+" ");
	    	ss.remove(ss.first());
	    	sb.append(ss.first()+"\n");
	    	ss.remove(ss.first());
		      
	    }	    pw.println(sb.toString());
	    
	    
	    
			}
	    
	    	     //-----------------------------------------The End--------------------------------------------------------------------------//
	    
	    	private static void dfs(int x1,int y1,char[][]a){
	    		boolean Visited[][]=new boolean[3][a[0].length];
	    		int level[][]=new int [3][a[0].length];
	    		Queue<Pair> s=new LinkedList<Pair>();
	    		s.add(new Pair(x1,y1));
	    		level[x1][y1]=0;
	    		int curr=0;
	    		while(!s.isEmpty()){
	    			Pair temp=s.poll();
	    			int x=temp.idx;
	    			int y=temp.val;
	    			Visited[x][y]=true;
	    	pw.println(x+" "+y+"___");
	    			if(curr!=level[x][y]){
	    				for(int i=0;i<3;i++){
	    					for(int j=0;j<a[0].length;j++){
	    						if(a[i][j]!='s' && a[i][j]!='.'){
	    						
	    							while(j<a[0].length && a[i][j]!='s' && a[i][j]!='.'){
	    								if(j>=2){
	    									a[i][j-2]=a[i][j];
	    									
	    								}
	    								a[i][j]='.';
	    							j++;
	    							}
	    							
	    						}
	    					}
	    				}
	    			
	    				curr=level[x][y];
	    			/*for(int i=0;i<3;i++){
	    					for(int j=0;j<a[0].length;j++){
	    						pw.print(a[i][j]);
	    					}
	    					pw.println();
	    				}
	    				pw.println();
	    		//	return;*/
	    			}
	    			if(( a[x][y]=='.' || a[x][y]=='s')){
	    				//pw.println(x+" "+y+"---");
	    			if( y==a[0].length-1){
	    				pw.println("YES");
	    				return;
	    			}
	    			if(check2(x+1, y+2, a) || check2(x-1, y+2, a)){
	    				s.add(new Pair(x,y));
	    			level[x][y]++;
	    			}else{
	    			if(check(x+1,y,a) ){
	    				s.add(new Pair(x+1,y));
	    				level[x+1][y]=level[x][y]+1;
	    			Visited[x+1][y]=true;
	    			}
	    			if(check(x,y+1,a) ){
	    				s.add(new Pair(x,y+1));
	    				level[x][y+1]=level[x][y]+1;
	    			Visited[x][y+1]=true;
	    			}if(check(x-1,y,a) ){
	    				level[x-1][y]=level[x][y]+1;
	    			Visited[x-1][y]=true;
	    			s.add(new Pair(x-1,y));
	    			}
	    			}
	    		
	    		}
	    			
	    		}	pw.println("NO");
	    	
	    	}
	    	private static boolean check2(int x,int y,char a[][]){
	    		if(x>=0 && y>=0 && x<3 && y<a[0].length && a[x][y]=='.')
	    			return true;
	    		return false;
	    	}
	    	private static boolean check(int x,int y,char a[][]){
	    		if(x>=0 && y>=0 && x<3 && y<a[0].length && a[x][y]=='.'){
	    			if(y<a[0].length-2 && a[x][y+2]=='.'){
	    				return true;
	    			}else
	    			return false;
	    			}
	    		return false;
	    	}
	    }
	    	
	   
	    
		class Pair implements Comparable<Pair>{
		     
			int idx,val;
			Pair(int idx,int val){
				this.idx=idx;
				this.val=val;
			}
			@Override
			public int compareTo(Pair o) {
				// TODO Auto-generated method stub
			//	Sort in increasing order
	 
			
				if(o.idx<idx){
					return 1;
				}
				if(o.idx==idx && o.val<val){
					return 1;
				}else{
					return -1;
				}
				
			}
			
		}
	        class Graph{
	        	private int V,level[][],count=-1,lev_dfs[],degree=0;
	        	private Stack <Integer>st=new Stack();
	        	private LinkedList<Integer > adj[];
	        	private boolean[][] Visite;
	        	private boolean [] Visited;
	        	private static TreeSet<Integer> ts=new TreeSet();
	    Graph(int V){
	    V++;
	    this.V=(V);
	    adj=new LinkedList[V];
	    Visite=new boolean[100][100];
	    Visited=new boolean[V];
	    
	    level=new int[100][100];
	   lev_dfs=new int[V]; 
	   for(int i=0;i<V;i++)
		   adj[i]=new LinkedList<Integer>();
	    }
	     
	    void addEdge(int v,int w){
	    	
	    	if(adj[v]==null){
	    		adj[v]=new LinkedList();
	    	}
	    	adj[v].add(w);
	     
	    	
	    }
	    public long getCount(long max){
	    	long pp=0;
	    	for(int i=1;i<V;i++){
	    		if(!Visited[i]){
	    			long d=dfs(i);
	    			pp+=(d*(d-1)/2)-getEd();
	    			pp+=d*max;
	    			max+=d;
	    			}
	    	}
	    	return pp;
	    }
	    public int getEd(){
	    	return degree/2;
	    }
	    public void get(int from,int to){
	    	int h=lev_dfs[from]-lev_dfs[to];
	    	if(h<=0){
	    		System.out.println(-1);
	    	}else{
	    		System.out.println(h-1);
	    	}
	    }
	    private static boolean check(int x,int y,char c[][]){
		
			if((x>=0 && y>=0) && (x<c.length && y<c[0].length) && c[x][y]!='#'){
				
				return true;
			}
			return false;
		}
	    public int BFS(int x,int y,int k,char[][] c)
	    {
	    	 LinkedList<Pair> queue = new LinkedList<Pair>();
	        //Visited[s]=true;
	        queue.add(new Pair(x,y));
	       int count=0;
	   level[x][y]=-1;
	   c[x][y]='M';
	        while (!queue.isEmpty())
	        {
	            Pair temp = queue.poll();
	            //x=temp.idx;
	            //y=temp.val;
	            
	            c[x][y]='M';
	      // System.out.println(x+" "+y+" ---"+count);
	         count++;
	     	if(count==k)
	         {
	         	for(int i=0;i<c.length;i++){
	         		for(int j=0;j<c[0].length;j++){
	         			if(c[i][j]=='M'){
	         				System.out.print(".");
	         			}
	         			else if(c[i][j]=='.')
	         				System.out.print("X");
	         			else
	         				System.out.print(c[i][j]);
	         		}
	         		System.out.println();
	         	}
	         System.exit(0);
	         }
	     	
	         // System.out.println(x+" "+y);
	           // V--;
	           
	        }
	        return V;
	    }
	    
	    
	     public long dfs(int startVertex){
	    	 ts.clear();
	    	 if(!Visited[startVertex])  {
	    
	    	return dfsUtil(startVertex,Visited);
	    	
	    	}
	    
	     
	    return 1;
	    	}
	     public String print_team(){
	    	 String s="";
	    	 if(ts.size()!=0)
	    	 s+=(ts.first()+" ");
	    	 ts.remove(ts.first());

	    	 if(ts.size()!=0)
	    	 s+=(ts.first()+" ");
	    	 ts.remove(ts.first());

	    	 if(ts.size()!=0)
	    	 s+=(ts.first()+" ");
	    	 return s;
	     }
	    private long dfsUtil(int startVertex, boolean[] Visited) {//0-Blue 1-Pink
	      long c=1;
	      degree=0;
	    	Visited[startVertex]=true; 
	    	lev_dfs[startVertex]=0;
	      st.push(startVertex);
	    while(!st.isEmpty()){
	    	int top=st.pop();
	    	ts.add(top);
	    	Iterator<Integer> i=adj[top].listIterator();
	     degree+=adj[top].size();
	    while(i.hasNext()){
	    //	System.out.println(top);
	    	int n=i.next();
	    		 if( !Visited[n]){
	    				Visited[n]=true;
	    					st.push(n);
	    					c++;
	    			
	    		 }
	    			 }
	    		
	    }
	    return c;
	    	
	    
	    
	    
	    }
	        
	        }     
	        	
	        
	    class Dsu{
	    	private int rank[], parent[] ,n;
	    	
	    	Dsu(int size){
	    		this.n=size+1;
	    		rank=new int[n];
	    		parent=new int[n];
	    	makeSet();
	    	}
	    	
	    	void makeSet(){
	    		for(int i=0;i<n;i++){
	    			parent[i]=i;
	    		}
	    	}
	    	
	    	int find(int x){
	    		if(parent[x]!=x){
	    			
	    			parent[x]=find(parent[x]);
	    		}
	    		return parent[x];
	    	}	
	    	
	    	void union(int x,int y){
	    		int xRoot=find(x);
	    		int yRoot=find(y);
	    		
	    		if(xRoot==yRoot)
	    			return;
	    		if(rank[xRoot]<rank[yRoot]){
	    		parent[xRoot]=yRoot;	
	    		}else if(rank[yRoot]<rank[xRoot]){
	    			parent[yRoot]=xRoot;
	    		}else{
	    			parent[yRoot]=xRoot;
	    			rank[xRoot]++;
	    		}
	    		
	    	}
	     
	    }
	    class Heap{
	    	
	    	public static void build_max_heap(long []a,int size){
	    		
	    		for(int i=size/2;i>0;i--){
	    			max_heapify(a, i,size);
	    		}
	    		
	    			}
	    	private static void max_heapify(long[] a,int i,int size){
	    		int left_child=2*i;
	    		int right_child=(2*i+1);
	    		int largest=0;
	    		
	    		if(left_child<size && a[left_child]>a[i]){
	    			largest=left_child;
	    		}else{
	    			largest=i;
	    		}
	    		
	    		if(right_child<size && a[right_child]>a[largest]){
	    			largest=right_child;
	    		}
	    		if(largest!=i){
	    			long temp=a[largest];
	    			a[largest]=a[i];
	    			a[i]=temp;
	    			max_heapify(a, largest,size);
	    		}
	    	}
	    	private static void min_heapify(int[] a,int i){
	    		int left_child=2*i;
	    		int right_child=(2*i+1);
	    		int largest=0;
	    		
	    		if(left_child<a.length && a[left_child]<a[i]){
	    			largest=left_child;
	    		}else{
	    			largest=i;
	    		}
	    		
	    		if(right_child<a.length && a[right_child]<a[largest]){
	    			largest=right_child;
	    		}
	    		if(largest!=i){
	    			int temp=a[largest];
	    			a[largest]=a[i];
	    			a[i]=temp;
	    			min_heapify(a, largest);
	    		}
	    	}
	    	public static void extract_max(int size,long a[]){
	    		if(a.length>1){
	    			long max=a[1];
	    			a[1]=a[a.length-1];
	    			size--;
	    			max_heapify(a, 1,a.length-1);
	    		}
	    	}
	    }
	    
	    class MyComp implements Comparator<Long>{
	        
			@Override
			public int compare(Long o1, Long o2) {
				if(o1<o2){
					return 1;
				}else if(o1>o2){
					return -1;
				}
				return 0;
				
			}
	    }