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:
import java.io.*;
import java.math.BigInteger;
import java.math.RoundingMode;
import java.text.DecimalFormat;
import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.net.ssl.SSLContext;

public class Main
{  
   static long mod=(long)(1e+9) + 7;  
   static int[] sieve;static int ans=0;
   static ArrayList<Integer> primes;
   static int visited[];
   static ArrayList<Integer> cur;
   
   public static void dfs(int start,ArrayList<Integer>[] graph)
   {
	   if(visited[start]==1) return ;
	   
	   visited[start]=1;
	   cur.add(start);
	   
	   for(int i=0;i<graph[start].size();i++)
		   dfs(graph[start].get(i),graph);
   }
   
   public static void main(String[] args) throws java.lang.Exception
   {	  	
	     fast s = new fast();
	     PrintWriter out=new PrintWriter(System.out);
	     Scanner sc=new Scanner(System.in);
	     StringBuilder fans = new StringBuilder();      
	   
	     int n=s.nextInt();
	     int m=s.nextInt();
	     
	     ArrayList<Integer>[] graph=new ArrayList[n+1];
	     ArrayList<ArrayList<Integer>>[] size=new ArrayList[n+1];
	     cur=new ArrayList<Integer>();
	     
	     for(int i=0;i<=n;i++) graph[i]=new ArrayList<Integer>();
	     for(int i=0;i<=n;i++) size[i]=new ArrayList<ArrayList<Integer>>();
	     
	     for(int i=0;i<m;i++)
	     {
	    	 int x=s.nextInt();
	    	 int y=s.nextInt();
	    	 graph[x].add(y);graph[y].add(x);
	     }
	     
	     visited=new int[n+1];
	     
	     for(int i=1;i<=n;i++)
	     {
	    	 if(visited[i]==0)
	    	 {
	    		 dfs(i,graph);
	    		 size[cur.size()].add(cur);
	    		 cur=new ArrayList<Integer>();    		 
	    	 }
	     }
	     
	     for(int i=4;i<=n;i++) if(size[i].size()>0) {System.out.println("-1"); return;}
	     if(size[2].size()>size[1].size()) {System.out.println("-1"); return;}
	     
	     for(int i=0;i<size[3].size();i++)
	     {
	    	 ArrayList<Integer> a=size[3].get(i);
	    	 fans.append(a.get(0)+" "+a.get(1)+" "+a.get(2));
	    	 fans.append("\n");
	     }
	     
	     if(size[2].size()==size[1].size())
	     {
	    	 for(int i=0;i<size[2].size();i++)
	    	 {
	    		 ArrayList<Integer> a=size[2].get(i);
	    		 ArrayList<Integer> b=size[1].get(i);
	    		 fans.append((a.get(0)+" "+a.get(1)+" "+b.get(0)));
	    		 fans.append("\n");
	    	 }
	     }
	     else
	     {
	    	 int diff=size[2].size()-size[1].size();
	    	 if(diff%3!=0) {System.out.println("-1"); return;}
	    	 
	    	 int ind=-1;
	    	 for(int i=0;i<size[2].size();i++)
	    	 {
	    		 ArrayList<Integer> a=size[2].get(i);
	    		 ArrayList<Integer> b=size[1].get(i);
	    		 fans.append((a.get(0)+" "+a.get(1)+" "+b.get(0)));
	    		 fans.append("\n");
	    		 ind=i;
	    	 }
	    	 
	    	 for(int i=ind+1;i<=size[1].size()-3;i+=3)
	    	 {
	    		 fans.append((size[1].get(i).get(0)+" "+size[1].get(i+1).get(0)+" "+size[1].get(i+2).get(0)));
	    		 fans.append("\n");
	    	 }    	 
	     }

    	 fans.deleteCharAt(fans.length()-1);     
	     System.out.println(fans);
   }
   
   
   

   static class fast {
		private InputStream i;
		private byte[] buf = new byte[1024];
		private int curChar;
		private int numChars;
		
		public static boolean next_permutation(int a[])
		   {
			   int i=0,j=0;int index=-1;	   
			   int n=a.length;
			   
			   for(i=0;i<n-1;i++)
				   if(a[i]<a[i+1]) index=i;
			   
			   if(index==-1) return false;
			   i=index;

			  
			   for(j=i+1;j<n && a[i]<a[j];j++);

			   int temp=a[i];
			   a[i]=a[j-1];
			   a[j-1]=temp;
			   	   
			   for(int p=i+1,q=n-1;p<q;p++,q--)
			   {
				   temp=a[p];
				   a[p]=a[q];
				   a[q]=temp;
			   }
			   
			   return true;
		   }
		   
		   
		public static void division(char ch[],int divisor)
		   {
			   int div=Character.getNumericValue(ch[0]); int mul=10;int remainder=0;
			   StringBuilder quotient=new StringBuilder("");
			   for(int i=1;i<ch.length;i++)
			   {
				   div=div*mul+Character.getNumericValue(ch[i]);	
				   if(div<divisor) {quotient.append("0");continue;}
				   quotient.append(div/divisor);
				   div=div%divisor;mul=10;
				   
			   } 
			   remainder=div;
			   while(quotient.charAt(0)=='0')quotient.deleteCharAt(0);	   
			   System.out.println(quotient+" "+remainder);	  
		   }
		
		public static void sieve(int size)
		{
			sieve=new int[size+1];
			primes=new ArrayList<Integer>();
			sieve[1]=1;
			for(int i=2;i<=Math.sqrt(size);i++)
			{
				if(sieve[i]==0)
				 {
					for(int j=i*i;j<size;j+=i) sieve[j]=1;
				 }
			}
			
			for(int i=2;i<=size;i++)
			{
				if(sieve[i]==0) primes.add(i);
			}
		}
		public static long pow(long n, long b, long MOD)
		   {
		       long x=1;long y=n; 
		       while(b > 0)
		       {
		           if(b%2 == 1)
		           {
		               x=x*y;
		               if(x>MOD) x=x%(MOD);
		           }
		           y = y*y;
		           if(y>MOD) y=y%(MOD); 
		           b >>= 1;
		       }
		       return x;
		   }

		
		 public static int lower(Integer[] a,int start,int end,int key)
		 {
			   int mid=(start+end)>>1;
			   if(start==end && a[mid]<key) {return -1;}
			   if(start>end) return -1;

			   if(a[mid]>=key && (((mid-1)>=0 && a[mid-1]<key) || (mid-1)==0)) return mid;
			   else if(a[mid]== key && (mid-1)>=0 && a[mid-1]==key) return lower(a,start,mid-1,key);   
			   else if(key>a[mid]) return lower(a,mid+1,end,key);
			   else return lower(a,start,mid-1,key);
		}
		 
		 public static int upper(Integer a[],int start,int end,int key)
		 {
			   int mid=(start+end)>>1;
			   if(start==end && a[mid]>key) {return -1;}
			   if(start>end) return -1;

			   if(a[mid]<=key && (((mid+1)<a.length && a[mid+1]>key) || (mid+1)==a.length)) return mid;
			   else if(a[mid]== key && (mid+1)<a.length && a[mid+1]==key) return upper(a,mid+1,end,key);   
			   else if(key>=a[mid]) return upper(a,mid+1,end,key);
			   else return upper(a,start,mid-1,key);
		} 
		   
		public int gcd(int a,int b)
		{
			if(a==0) return b;
			return gcd(b%a,a);
		}
		public fast() {
			this(System.in);
		}
		public fast(InputStream is) {
			i = is;
		}
		public int read() {
			if (numChars == -1)
				throw new InputMismatchException();
			if (curChar >= numChars) {
				curChar = 0;
				try {
					numChars = i.read(buf);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (numChars <= 0)
					return -1;
			}
			return buf[curChar++];
		}
		public 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();
		}
		public String nextString() {
     		int c = read();
			while (isSpaceChar(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isSpaceChar(c));
			return res.toString();
		}
		public 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;
		}
		public 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;
		}
		public boolean isSpaceChar(int c) {
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}
		public boolean isEndOfLine(int c) {
			return c == '\n' || c == '\r' || c == -1;
		}

	}	
}