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.OutputStreamWriter;
import java.io.BufferedWriter;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.Writer;
import java.util.List;
import java.io.IOException;
import java.util.InputMismatchException;
import java.util.ArrayList;
import java.util.NoSuchElementException;
import java.math.BigInteger;
import java.util.Collections;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 * @author Egor Kulikov (egor@egork.net)
 */
public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		OutputWriter out = new OutputWriter(outputStream);
		TaskB solver = new TaskB();
		solver.solve(1, in, out);
		out.close();
	}
}

class TaskB {
    public void solve(int testNumber, InputReader in, OutputWriter out) {
		int count = in.readInt();
		int edgeCount = in.readInt();
		int[] from = new int[edgeCount];
		int[] to = new int[edgeCount];
		IOUtils.readIntArrays(in, from, to);
		MiscUtils.decreaseByOne(from, to);
		IndependentSetSystem setSystem = new RecursiveIndependentSetSystem(count);
		for (int i = 0; i < edgeCount; i++)
			setSystem.join(from[i], to[i]);
		IntList[] teams = new IntList[count];
		for (int i = 0; i < count; i++)
			teams[i] = new IntArrayList();
		for (int i = 0; i < count; i++)
			teams[setSystem.get(i)].add(i + 1);
		List<IntList> answer = new ArrayList<IntList>();
		List<IntList> pair = new ArrayList<IntList>();
		List<IntList> single = new ArrayList<IntList>();
		for (IntList team : teams) {
			if (team.size() > 3) {
				out.printLine(-1);
				return;
			}
			if (team.size() == 3)
				answer.add(team);
			if (team.size() == 2)
				pair.add(team);
			if (team.size() == 1)
				single.add(team);
		}
		if (pair.size() > single.size()) {
			out.printLine(-1);
			return;
		}
		for (int i = 0; i < pair.size(); i++) {
			IntList current = pair.get(i);
			current.addAll(single.get(i));
			answer.add(current);
		}
		for (int i = pair.size(); i < single.size(); i += 3) {
			IntList current = single.get(i);
			current.addAll(single.get(i + 1));
			current.addAll(single.get(i + 2));
			answer.add(current);
		}
		for (IntList team : answer)
			out.printLine(team);
    }
}

class InputReader {

	private InputStream stream;
	private byte[] buf = new byte[1024];
	private int curChar;
	private int numChars;
	private SpaceCharFilter filter;

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

	public 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++];
	}

	public int readInt() {
		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) {
		if (filter != null)
			return filter.isSpaceChar(c);
		return isWhitespace(c);
	}

	public static boolean isWhitespace(int c) {
		return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
	}

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

class OutputWriter {
	private final PrintWriter writer;

	public OutputWriter(OutputStream outputStream) {
		writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
	}

	public OutputWriter(Writer writer) {
		this.writer = new PrintWriter(writer);
	}

	public void print(Object...objects) {
		for (int i = 0; i < objects.length; i++) {
			if (i != 0)
				writer.print(' ');
			writer.print(objects[i]);
		}
	}

    public void print(IntCollection collection) {
		boolean first = true;
		for (IntIterator iterator = collection.iterator(); iterator.isValid(); iterator.advance()) {
			if (first)
				first = false;
			else
				writer.print(' ');
			writer.print(iterator.value());
		}
	}

	public void printLine(IntCollection collection) {
		print(collection);
		writer.println();
	}

	public void printLine(Object...objects) {
		print(objects);
		writer.println();
	}

	public void close() {
		writer.close();
	}

	}

class IOUtils {

	public static void readIntArrays(InputReader in, int[]... arrays) {
		for (int i = 0; i < arrays[0].length; i++) {
			for (int j = 0; j < arrays.length; j++)
				arrays[j][i] = in.readInt();
		}
	}

	}

class MiscUtils {

    public static void decreaseByOne(int[]...arrays) {
		for (int[] array : arrays) {
			for (int i = 0; i < array.length; i++)
				array[i]--;
		}
	}

	}

interface IndependentSetSystem {
	public boolean join(int first, int second);

	public int get(int index);

	public static interface Listener {
		public void joined(int joinedRoot, int root);
	}
}

class RecursiveIndependentSetSystem implements IndependentSetSystem {
	private final int[] color;
	private int setCount;
	private Listener listener;

	public RecursiveIndependentSetSystem(int size) {
		color = new int[size];
		for (int i = 0; i < size; i++)
			color[i] = i;
		setCount = size;
	}

	public RecursiveIndependentSetSystem(RecursiveIndependentSetSystem other) {
		color = other.color.clone();
		setCount = other.setCount;
	}

	public boolean join(int first, int second) {
		first = get(first);
		second = get(second);
		if (first == second)
			return false;
		setCount--;
		color[second] = first;
		if (listener != null)
			listener.joined(second, first);
		return true;
	}

	public int get(int index) {
		if (color[index] == index)
			return index;
		return color[index] = get(color[index]);
	}

	}

abstract class IntList extends IntCollection implements Comparable<IntList> {
	private static final int INSERTION_THRESHOLD = 8;

	public abstract int get(int index);
	public abstract void set(int index, int value);

	public IntIterator iterator() {
		return new IntIterator() {
			private int size = size();
			private int index = 0;

			public int value() throws NoSuchElementException {
				if (!isValid())
					throw new NoSuchElementException();
				return get(index);
			}

			public void advance() throws NoSuchElementException {
				if (!isValid())
					throw new NoSuchElementException();
				index++;
			}

			public boolean isValid() {
				return index < size;
			}
		};
	}

	private void swap(int first, int second) {
		if (first == second)
			return;
		int temp = get(first);
		set(first, get(second));
		set(second, temp);
	}

	public IntSortedList inPlaceSort(IntComparator comparator) {
		quickSort(0, size() - 1, size(), comparator);
		return new IntSortedArray(this, comparator);
	}

	private void quickSort(int from, int to, int remaining, IntComparator comparator) {
		if (to - from < INSERTION_THRESHOLD) {
			insertionSort(from, to, comparator);
			return;
		}
		if (remaining == 0) {
			heapSort(from, to, comparator);
			return;
		}
		remaining >>= 1;
		int pivotIndex = (from + to) >> 1;
		int pivot = get(pivotIndex);
		swap(pivotIndex, to);
		int storeIndex = from;
		int equalIndex = to;
		for (int i = from; i < equalIndex; i++) {
			int value = comparator.compare(get(i), pivot);
			if (value < 0)
				swap(storeIndex++, i);
			else if (value == 0)
				swap(--equalIndex, i--);
		}
		quickSort(from, storeIndex - 1, remaining, comparator);
		for (int i = equalIndex; i <= to; i++)
			swap(storeIndex++, i);
		quickSort(storeIndex, to, remaining, comparator);
	}

	private void heapSort(int from, int to, IntComparator comparator) {
		for (int i = (to + from - 1) >> 1; i >= from; i--)
			siftDown(i, to, comparator, from);
		for (int i = to; i > from; i--) {
			swap(from, i);
			siftDown(from, i - 1, comparator, from);
		}
	}

	private void siftDown(int start, int end, IntComparator comparator, int delta) {
		int value = get(start);
		while (true) {
			int child = ((start - delta) << 1) + 1 + delta;
			if (child > end)
				return;
			int childValue = get(child);
			if (child + 1 <= end) {
				int otherValue = get(child + 1);
				if (comparator.compare(otherValue, childValue) > 0) {
					child++;
					childValue = otherValue;
				}
			}
			if (comparator.compare(value, childValue) >= 0)
				return;
			swap(start, child);
			start = child;
		}
	}

	private void insertionSort(int from, int to, IntComparator comparator) {
		for (int i = from + 1; i <= to; i++) {
			int value = get(i);
			for (int j = i - 1; j >= from; j--) {
				if (comparator.compare(get(j), value) <= 0)
					break;
				swap(j, j + 1);
			}
		}
	}

	public IntSortedList sort(IntComparator comparator) {
		return new IntArray(this).inPlaceSort(comparator);
	}

	public int hashCode() {
		int hashCode = 1;
		for (IntIterator i = iterator(); i.isValid(); i.advance())
			hashCode = 31 * hashCode + i.value();
		return hashCode;
	}

	public boolean equals(Object obj) {
		if (!(obj instanceof IntList))
			return false;
		IntList list = (IntList)obj;
		if (list.size() != size())
			return false;
		IntIterator i = iterator();
		IntIterator j = list.iterator();
		while (i.isValid()) {
			if (i.value() != j.value())
				return false;
			i.advance();
			j.advance();
		}
		return true;
	}

	public int compareTo(IntList o) {
		IntIterator i = iterator();
		IntIterator j = o.iterator();
		while (true) {
			if (i.isValid()) {
				if (j.isValid()) {
					if (i.value() != j.value()) {
						if (i.value() < j.value())
							return -1;
						else
							return 1;
					}
				} else
					return 1;
			} else {
				if (j.isValid())
					return -1;
				else
					return 0;
			}
			i.advance();
			j.advance();
		}
	}

	}

class IntArrayList extends IntList {
	private int[] array;
	private int size;

	public IntArrayList() {
		this(10);
	}

	public IntArrayList(int capacity) {
		array = new int[capacity];
	}

	public int get(int index) {
		if (index >= size)
			throw new IndexOutOfBoundsException();
		return array[index];
	}

	public void set(int index, int value) {
		if (index >= size)
			throw new IndexOutOfBoundsException();
		array[index] = value;
	}

	public int size() {
		return size;
	}

	public void add(int value) {
		ensureCapacity(size + 1);
		array[size++] = value;
	}

	private void ensureCapacity(int newCapacity) {
		if (newCapacity > array.length) {
			int[] newArray = new int[Math.max(newCapacity, array.length << 1)];
			System.arraycopy(array, 0, newArray, 0, size);
			array = newArray;
		}
	}

	}

abstract class IntCollection {
	public abstract IntIterator iterator();
	public abstract int size();
	public abstract void add(int value);

	public void addAll(IntCollection values) {
		for (IntIterator it = values.iterator(); it.isValid(); it.advance()) {
			add(it.value());
		}
	}

	}

interface IntIterator {
	public int value() throws NoSuchElementException;
	/*
	 * @throws NoSuchElementException only if iterator already invalid
	 */
	public void advance() throws NoSuchElementException;
	public boolean isValid();
}

interface IntComparator {
    public static final IntComparator DEFAULT = new IntComparator() {
        public int compare(int first, int second) {
            if (first < second)
                return -1;
            if (first > second)
                return 1;
            return 0;
        }
    };

	public int compare(int first, int second);
}

abstract class IntSortedList extends IntList {
	protected final IntComparator comparator;

	protected IntSortedList(IntComparator comparator) {
		this.comparator = comparator;
	}

	public void set(int index, int value) {
		throw new UnsupportedOperationException();
	}

	public void add(int value) {
		throw new UnsupportedOperationException();
	}

	public IntSortedList inPlaceSort(IntComparator comparator) {
		if (comparator == this.comparator)
			return this;
		throw new UnsupportedOperationException();
	}

	public IntSortedList sort(IntComparator comparator) {
		if (comparator == this.comparator)
			return this;
		return super.sort(comparator);
	}

	protected void ensureSorted() {
		int size = size();
		if (size == 0)
			return;
		int last = get(0);
		for (int i = 1; i < size; i++) {
			int current = get(i);
			if (comparator.compare(last, current) > 0)
				throw new IllegalArgumentException();
			last = current;
		}
	}

	}

class IntSortedArray extends IntSortedList {
	private final int[] array;

	public IntSortedArray(int[] array) {
		this(array, IntComparator.DEFAULT);
	}

	public IntSortedArray(IntCollection collection) {
		this(collection, IntComparator.DEFAULT);
	}

	public IntSortedArray(int[] array, IntComparator comparator) {
		super(comparator);
		this.array = array;
		ensureSorted();
	}

	public IntSortedArray(IntCollection collection, IntComparator comparator) {
		super(comparator);
		array = new int[collection.size()];
		int i = 0;
		for (IntIterator iterator = collection.iterator(); iterator.isValid(); iterator.advance())
			array[i++] = iterator.value();
		ensureSorted();
	}

	public int get(int index) {
		return array[index];
	}

	public int size() {
		return array.length;
	}
}

class IntArray extends IntList {
	private final int[] array;

	public IntArray(int[] array) {
		this.array = array;
	}

	public IntArray(IntCollection collection) {
		array = new int[collection.size()];
		int i = 0;
		for (IntIterator iterator = collection.iterator(); iterator.isValid(); iterator.advance())
			array[i++] = iterator.value();
	}

	public int get(int index) {
		return array[index];
	}

	public void set(int index, int value) {
		array[index] = value;
	}

	public int size() {
		return array.length;
	}

	public void add(int value) {
		throw new UnsupportedOperationException();
	}

	}