Problem: Student Vladislav came to his programming exam completely unprepared as usual. He got a question about some strange algorithm on a graph — something that will definitely never be useful in real life. He asked a girl sitting next to him to lend him some cheat papers for this questions and found there the following definition:

The minimum spanning tree T of graph G is such a tree that it contains all the vertices of the original graph G, and the sum of the weights of its edges is the minimum possible among all such trees.

Vladislav drew a graph with n vertices and m edges containing no loops and multiple edges. He found one of its minimum spanning trees and then wrote for each edge its weight and whether it is included in the found tree or not. Unfortunately, the piece of paper where the graph was painted is gone and the teacher is getting very angry and demands to see the original graph. Help Vladislav come up with a graph so that the information about the minimum spanning tree remains correct.

Input

The first line of the input contains two integers n and m (<image>) — the number of vertices and the number of edges in the graph.

Each of the next m lines describes an edge of the graph and consists of two integers aj and bj (1 ≤ aj ≤ 109, bj = {0, 1}). The first of these numbers is the weight of the edge and the second number is equal to 1 if this edge was included in the minimum spanning tree found by Vladislav, or 0 if it was not.

It is guaranteed that exactly n - 1 number {bj} are equal to one and exactly m - n + 1 of them are equal to zero.

Output

If Vladislav has made a mistake and such graph doesn't exist, print  - 1.

Otherwise print m lines. On the j-th line print a pair of vertices (uj, vj) (1 ≤ uj, vj ≤ n, uj ≠ vj), that should be connected by the j-th edge. The edges are numbered in the same order as in the input. The graph, determined by these edges, must be connected, contain no loops or multiple edges and its edges with bj = 1 must define the minimum spanning tree. In case there are multiple possible solutions, print any of them.

Examples

Input

4 5
2 1
3 1
4 0
1 1
5 0


Output

2 4
1 4
3 4
3 1
3 2


Input

3 3
1 0
2 1
3 1


Output

-1

Solution (in JAVA):

Solution:
//package com.codeforces.competitions.year2015.octobertodecember.round335div2;

import java.awt.*;
import java.io.*;
import java.util.*;

public final class Q4
{
	public static void main(String[] args)
	{
		InputReader in = new InputReader(System.in);
		OutputWriter out = new OutputWriter(System.out);

		Solver solver = new Solver(in, out);
		solver.solve();
		
		out.flush();
		
		in.close();
		out.close();
	}

	static class Solver
	{
		int n, m;
		Edge[] edges, copy;
		HashMap<Integer, Integer> count;
		InputReader in;
		OutputWriter out;

		void solve()
		{
			n = in.nextInt();
			m = in.nextInt();
			edges = new Edge[m];
			copy = new Edge[m];

			for (int i = 0; i < m; i++)
			{
				int weight, used;

				weight = in.nextInt();
				used = in.nextInt();

/*				edges[i] = new Edge(i, weight, used == 1);
				copy[i] = new Edge(i, weight, used == 1);*/

				edges[i] = new Edge(i, weight, used);
				copy[i] = new Edge(i, weight, used);
			}

			compress();

			int[] weight = new int[n + 1];
			int counter = 2;

			for (int i = 0; i < m; i++)
			{
//				if (edges[i].used)
				if (edges[i].used == 1)
					weight[counter++] = edges[i].weight;
			}

			Deque<Left> deque = new ArrayDeque<>();
			Deque<Point> pointDeque = new ArrayDeque<>();
//			int counter = 1;

			counter = 1;

			for (int i = 0; i < m; i++)
			{
/*				System.out.println("i : " + i + ", edges[i] => wt : " + edges[i].weight + ", used : " + edges[i].used
						+ ", pointDeque : " + pointDeque.toString());*/

				if (edges[i].used == 0)
				{
					if (pointDeque.size() == 0)
					{
						out.println(-1);

						return;
					}

					Point first = pointDeque.pollFirst();

					if (edges[i].weight < weight[first.y])
					{
						out.println(-1);

						return;
					}

					edges[i].from = first.x;
					edges[i].to = first.y;

					first.x++;

					if (first.x < first.y - 1)
						pointDeque.addFirst(first);
				}
				else
				{
					edges[i].from = counter;
					edges[i].to = ++counter;

					if (i > 0)
						pointDeque.addLast(new Point(1, counter));
				}
			}

/*			for (int i = 0; i < m; i++)
			{
				int curr = edges[i].weight;
				int occurrences = count.get(curr);
				int possible = occurrences - 1 + n - 2 - i;
				count.put(curr, possible);

//				if (!edges[i].used)
				if (edges[i].used == 0)
				{
					if (deque.size() == 0)
					{
						out.println(-1);

						return;
					}

					edges[i].to = n + 1;
					Left leftOver = null;

					while (edges[i].to > n)
					{
						leftOver = deque.poll();

						edges[i].from = leftOver.from;
						edges[i].to = leftOver.from + leftOver.used + 2;
					}

					if (edges[i].weight < weight[edges[i].to])
					{
						out.println(-1);

						return;
					}

					leftOver.used++;

					if (leftOver.used < leftOver.total)
						deque.addFirst(leftOver);
				}
				else
				{
					edges[i].from = counter;
					edges[i].to = ++counter;
				}

				if (possible > 0)
					deque.add(new Left(i + 1, possible, 0));
			}*/

			Arrays.sort(edges, new Comparator<Edge>()
			{
				@Override public int compare(Edge o1, Edge o2)
				{
					return Integer.compare(o1.index, o2.index);
				}
			});

			for (int i = 0; i < m; i++)
				out.println(edges[i].from + " " + edges[i].to);
		}

		void compress()
		{
			Arrays.sort(copy, new Comparator<Edge>()
			{
				@Override public int compare(Edge o1, Edge o2)
				{
					return Integer.compare(o1.weight, o2.weight);
				}
			});

			HashMap<Integer, Integer> map = new HashMap<>();
			int counter = 1;

			for (int i = 0; i < m; i++)
				if (!map.containsKey(copy[i].weight))
					map.put(copy[i].weight, counter++);

//			System.out.println("mapping : " + map.toString());

			count = new HashMap<>();

			for (int i = 0; i < m; i++)
			{
				int mapping = map.get(edges[i].weight);
				Integer temp = count.get(mapping);

				edges[i].weight = mapping;

				if (temp == null)
					count.put(mapping, 1);
				else
					count.put(mapping, temp + 1);
			}

			Arrays.sort(edges, new Comparator<Edge>()
			{
				@Override public int compare(Edge o1, Edge o2)
				{
					if (o1.weight == o2.weight)
					{
						return Integer.compare(o2.used, o1.used);
/*						if (o1.used && o2.used)
							return 0;

						if (o1.used)
							return -1;

						return 1;*/
					}

					return Integer.compare(o1.weight, o2.weight);
				}
			});
		}

		class Edge
		{
			int index, weight, from, to;
			int used;

			public Edge(int index, int weight, int used)
			{
				this.index = index;
				this.weight = weight;
				this.used = used;
			}

/*			boolean used;

			public Edge(int index, int weight, boolean used)
			{
				this.index = index;
				this.weight = weight;
				this.used = used;
			}*/

		}

		class Left
		{
			int from, total, used;

			public Left(int from, int total, int used)
			{
				this.from = from;
				this.total = total;
				this.used = used;
			}

		}

		public Solver(InputReader in, OutputWriter out)
		{
			this.in = in;
			this.out = out;
		}

	}
	
	static class InputReader
	{
		private InputStream stream;
		private byte[] buf = new byte[1024];
		private int curChar;
		private int numChars;

		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 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 & 15;

				c = read();
			} while (!isSpaceChar(c));

			return res * sgn;
		}
		
		public int[] nextIntArray(int arraySize)
		{
			int array[] = new int[arraySize];
			
			for (int i = 0; i < arraySize; i++)
				array[i] = nextInt();
			
			return array;
		}

		public long nextLong()
		{
			int c = read();

			while (isSpaceChar(c))
				c = read();

			int sign = 1;

			if (c == '-')
			{
				sign = -1;

				c = read();
			}

			long result = 0;

			do
			{
				if (c < '0' || c > '9')
					throw new InputMismatchException();

				result *= 10;
				result += c & 15;

				c = read();
			} while (!isSpaceChar(c));

			return result * sign;
		}
		
		public long[] nextLongArray(int arraySize)
		{
			long array[] = new long[arraySize];
			
			for (int i = 0; i < arraySize; i++)
				array[i] = nextLong();
			
			return array;
		}

		public float nextFloat() // problematic
		{
			float result, div;
			byte c;

			result = 0;
			div = 1;
			c = (byte) read();

			while (c <= ' ')
				c = (byte) read();

			boolean isNegative = (c == '-');

			if (isNegative)
				c = (byte) read();

			do
			{
				result = result * 10 + c - '0';
			} while ((c = (byte) read()) >= '0' && c <= '9');

			if (c == '.')
				while ((c = (byte) read()) >= '0' && c <= '9')
					result += (c - '0') / (div *= 10);

			if (isNegative)
				return -result;

			return result;
		}

		public double nextDouble() // not completely accurate
		{
			double ret = 0, div = 1;
			byte c = (byte) read();

			while (c <= ' ')
				c = (byte) read();

			boolean neg = (c == '-');

			if (neg)
				c = (byte) read();

			do
			{
				ret = ret * 10 + c - '0';
			} while ((c = (byte) read()) >= '0' && c <= '9');

			if (c == '.')
				while ((c = (byte) read()) >= '0' && c <= '9')
					ret += (c - '0') / (div *= 10);

			if (neg)
				return -ret;

			return ret;
		}

		public String next()
		{
			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 boolean isSpaceChar(int c)
		{
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}
		
		public String nextLine()
		{
			int c = read();
			
			StringBuilder result = new StringBuilder();
			
			do
			{
				result.appendCodePoint(c);
				
				c = read();
			} while (!isNewLine(c));
			
			return result.toString();
		}
		
		public boolean isNewLine(int c)
		{
			return c == '\n';
		}

		public void close()
		{
			try
			{
				stream.close();
			}
			catch (IOException e)
			{
				e.printStackTrace();
			}
		}

	}

	static class OutputWriter
	{
		private PrintWriter writer;

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

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

		public void println(int x)
		{
			writer.println(x);
		}

		public void print(int x)
		{
			writer.print(x);
		}

		public void println(int array[], int size)
		{
			for (int i = 0; i < size; i++)
				println(array[i]);
		}

		public void print(int array[], int size)
		{
			for (int i = 0; i < size; i++)
				print(array[i] + " ");
		}

		public void println(long x)
		{
			writer.println(x);
		}

		public void print(long x)
		{
			writer.print(x);
		}

		public void println(long array[], int size)
		{
			for (int i = 0; i < size; i++)
				println(array[i]);
		}

		public void print(long array[], int size)
		{
			for (int i = 0; i < size; i++)
				print(array[i]);
		}

		public void println(float num)
		{
			writer.println(num);
		}

		public void print(float num)
		{
			writer.print(num);
		}

		public void println(double num)
		{
			writer.println(num);
		}

		public void print(double num)
		{
			writer.print(num);
		}

		public void println(String s)
		{
			writer.println(s);
		}

		public void print(String s)
		{
			writer.print(s);
		}

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

		public void printSpace()
		{
			writer.print(" ");
		}

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

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

	}

}

/*

4 4
4 1
5 1
7 0
8 1

4 4
4 1
5 0
7 1
8 1

10 15
900000012 1
900000010 1
900000007 0
900000005 0
900000014 1
900000000 1
900000004 0
900000006 1
900000009 0
900000002 0
900000008 0
900000001 1
900000011 1
900000003 1
900000013 1


*/