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.util.*;
import java.text.*;
import java.lang.*;
import java.lang.reflect.Array;
import java.math.BigInteger;
import java.util.regex.*;
public class Main {
           public static ArrayList a[]=new ArrayList[300001];
           public static boolean visit[]=new boolean [5000001];
          static int parent[]=new int[100001];
          static void ini() {
        	  for(int i=0;i<100;i++)
        		  parent[i]=i;
          }
          static int root(int n) {
        	  while(parent[n]!=n) {
        		  n=parent[n];
        	  }
        	  return n;
          }
          static void union(int a,int b) {
        	  int p1=root(a);
        	  int p2=root(b);
        	  parent[p1]=parent[p2];
          }
          static boolean find(int a,int b) {
        	  if(root(a)==root(b))
        		  return true;
        	  else
        		  return false;
          }
			public static void main(String[] args) 
	        {
	            InputReader in = new InputReader(System.in);
	            PrintWriter pw = new PrintWriter(System.out);
	            int n=in.nextInt();
	            ini();
	            Vector<Integer>three=new Vector<>();
	            Vector<Integer>two=new Vector<>();
	            Vector<Integer>one=new Vector<>(); 
	            for(int i=0;i<=n;i++)
	            	a[i]=new ArrayList<Integer>();
	            int m=in.nextInt();
	            for(int i=0;i<m;i++) {
	            	int x=in.nextInt();
	            	int y=in.nextInt();
	            	union(x,y);
	            }
	            boolean chk[]=new boolean [n+1];
	            for(int i=1;i<=n;i++) {
	            	if(!chk[i]) {
	            		a[i].add(i);
		            	for(int j=i+1;j<=n;j++) {
		            		if(find(i,j)) {
		            			a[i].add(j);
		            			chk[j]=true;
		            		}
		            	}
		            	chk[i]=true;
	            	}
	            }
	            
	            boolean fi=true;
	            for(int i=1;i<=n;i++) {
	            	if(a[i].size()==3)
	            		three.add(i);
	            	if(a[i].size()==2)
	            		two.add(i);
	            	if(a[i].size()==1)
	            		one.add(i);
	            	else if(a[i].size()>3)
	            		fi=false;
	            }
	            
	            if(two.size()>one.size())
	            	fi=false;
	            if(!fi)
	            {
	            	pw.println(-1);
	            	pw.flush();
	            	pw.close();
	            	System.exit(0);
	            }
	            Vector<Integer>ans=new Vector<>();
	            for(int i=0;i<three.size();i++) {
	            	for(int j=0;j<a[three.get(i)].size();j++)
	            		ans.add((Integer) a[three.get(i)].get(j));
	            }
	            int i=0;
	            for( i=0;i<two.size();i++) {
	            	for(int j=0;j<a[two.get(i)].size();j++) {
	            		ans.add((Integer) a[two.get(i)].get(j));
	            	}
	            	for(int j=0;j<a[one.get(i)].size();j++) {
	            		ans.add((Integer) a[one.get(i)].get(j));
	            	}
	            }
	            for( ;i<one.size();i++) {
	            for(int j=0;j<a[one.get(i)].size();j++) {
            		ans.add((Integer) a[one.get(i)].get(j));
            	}
	        }
	            if(!fi)
	            	pw.println(-1);
	            else
	            	for( i=0;i<ans.size();) {
	            		for(int j=0;j<3;j++) {
	            			pw.print(ans.get(i+j)+" ");
	            		}
	            		i+=3;
	            	}
	            pw.flush();
	            pw.close();
	        
	        }
		private static void debug(Object... o) {
			System.out.println(Arrays.deepToString(o));
		}
		static class trie{
			
			Integer cnt;
			trie a[];
			trie(){
				cnt=0;
			    a=new trie[2];
			}
			
		}
        static class InputReader 
        {
        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 nextInt() 
        {
            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 nextLong()
        {
            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] = nextInt();
            }
            return a;
        }
        static class tri implements Comparable<tri> {
            int p, c, l;
 
            tri(int p, int c, int l) {
                this.p = p;
                this.c = c;
                this.l = l;
            }
 
            public int compareTo(tri o) {
                return Integer.compare(l, o.l);
            }
        }
 
        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);
        }
    }
        public static long mod = 1000000007;
        public static long d;
        public static long p;
        public static long q;
        
        public static int[] suffle(int[] a,Random gen)
        {
            int n = a.length;
            for(int i=0;i<n;i++)
            {
                int ind = gen.nextInt(n-i)+i;
                int temp = a[ind];
                a[ind] = a[i];
                a[i] = temp;
            }
            return a;
        }
        
        public static void swap(int a, int b){
            int temp = a;
            a = b;
            b = temp;
        }
        
        public static HashSet<Integer> primeFactorization(int n)
        {
            HashSet<Integer> a =new HashSet<Integer>();
            for(int i=2;i*i<=n;i++)
            {
                while(n%i==0)
                {
                    a.add(i);
                    n/=i;
                }
            }
            if(n!=1)
                a.add(n);
            return a;
        }
        
        public static void sieve(boolean[] isPrime,int n)
        {
            for(int i=1;i<n;i++)
                isPrime[i] = true;
            
            isPrime[0] = false;
            isPrime[1] = false;
            
            for(int i=2;i*i<n;i++)
            {
                if(isPrime[i] == true)
                {
                    for(int j=(2*i);j<n;j+=i)
                        isPrime[j] = false;
                }
            }
        }
        
        public static int GCD(int a,int b)
        {
            if(b==0)
                return a;
            else
                return GCD(b,a%b);
        }
        
        
        public static long GCD(long a,long b)
        {
            if(b==0)
                return a;
            else
                return GCD(b,a%b);
        }
        
        public static void extendedEuclid(long d1,long d2)
        {
            if(d2==0)
            {
                d = d1;
                p = 1 ;
                q = 0;
            }
            else
            {
                extendedEuclid(d2, d1%d2);
                long temp = p;
                p = q;
                q = temp - (d1/d2)*q;
            }
        }
        
        public static long LCM(long a,long b)
        {
            return (a*b)/GCD(a,b);
        }
        
        public static int LCM(int a,int b)
        {
            return (a*b)/GCD(a,b);
        }
        
        public static int binaryExponentiation(int x,int n)
        {
            int result=1;
            while(n>0)
            {
                if(n % 2 ==1)
                    result=result * x;
                x=x*x;
                n=n/2;
            }
            return result;
        }
        
        public static long binaryExponentiation(long x,long n)
        {
            long result=1;
            while(n>0)
            {
                if(n % 2 ==1)
                    result=result * x;
                x=x*x;
                n=n/2;
            }
            return result;
        }
        
        public static int modularExponentiation(int x,int n,int M)
        {
            int result=1;
            while(n>0)
            {
                if(n % 2 ==1)
                    result=(result * x)%M;
                x=(x%M*x)%M;
                n=n/2;
            }
            return result;
        }
        
        public static long modularExponentiation(long x,long n,long M)
        {
            long result=1;
            while(n>0)
            {
                if(n % 2 ==1)
                    result=(result%M * x%M)%M;
                x=(x%M * x%M)%M;
                n=n/2;
            }
            return result;
        }
        
        public static long modInverse(int A,int M)
        {
            return modularExponentiation(A,M-2,M);
        }
        
        public static long modInverse(long A,long M)
        {
            return modularExponentiation(A,M-2,M);
        }
        
        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;
        }
        
         public static pair[] shuffle(pair[] t, Random gen){ 
                for(int i = 0, n = t.length;i < n;i++){ 
                    int ind = gen.nextInt(n-i)+i; 
                    pair d = t[i]; 
                    t[i] = t[ind]; 
                    t[ind] = d; 
                } 
                return t; 
            }
        static class pair implements Comparable<pair>
        {
            Long x;
            Integer y;
            pair(long a,int w)
            {
                this.x=a;
                this.y=w;
            }
 

 
 
 
 
 
        public int compareTo(pair o) {
                int result = x.compareTo(o.x);
                if(result==0)
                    result = y.compareTo(o.y);
                return result;
            }  
            
            public String toString()
            {
                return x+" "+y;
            }
            
            public boolean equals(Object o)
            {
                if (o instanceof pair)
                {
                    pair p = (pair)o;
                    return p.x == x && p.y == y ;
                }
                return false;
            }
            
            public int hashCode()
            {
                return new Long(x).hashCode()*31 + new Long(y).hashCode();
            }
        }
        
}