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:
import java.io.*;
import java.util.*;
import java.util.concurrent.TimeUnit;

public class a implements Runnable{
	
    public static void main(String[] args) {
    	try{
            new Thread(null, new a(), "process", 1<<26).start();
        }
        catch(Exception e){
            System.out.println(e);
        }
    }
	public void run() {
		FastReader scan = new FastReader();
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
		//PrintWriter out = new PrintWriter("file.out");
		Task solver = new Task();
		//int t = scan.nextInt();
		int t = 1;
		for(int i = 1; i <= t; i++) solver.solve(i, scan, out);
		out.close();
	}

	static class Task {
		static final int inf = Integer.MAX_VALUE;

		static List<List<tup>> adj;
		public void solve(int testNumber, FastReader sc, PrintWriter out) {
			int N = sc.nextInt();
			int M = sc.nextInt();
			
			PriorityQueue<tup> edges = new PriorityQueue<tup>(new tup());
			for(int i = 0; i < M; i++) {
				edges.add(new tup(i, sc.nextInt(), sc.nextInt()));
			}
			
			int currentNode = 2;
			adj = new ArrayList<>();
			adj.add(new ArrayList<>());
			adj.add(new ArrayList<>());
			
			Queue<tup> possible = new LinkedList<>();
			
			while(edges.size() > 0) {
				tup edge = edges.poll();
				if(edge.id == 1){
					if(currentNode > N) {
						out.println(-1);
						return;
					}
					adj.add(new ArrayList<>());
					adj.get(1).add(new tup(currentNode, edge.a, 0));
					adj.get(currentNode).add(new tup(1, edge.a, 0));
					
					if(possible.size() < M) {
						for(int i = 2; i < currentNode; i++) {
							possible.add(new tup(currentNode, i, 0));
						}
					}
						
					currentNode++;

				} else {
					if(possible.size() == 0) {
						out.println(-1);
						return;
					}
					tup ed = possible.poll();
					adj.get(ed.a).add(new tup(ed.b, edge.a, 0));
					adj.get(ed.b).add(new tup(ed.a, edge.a, 0));
				}
			}
			
			//System.out.println(adj);
			tup[] eds = new tup[M];
			for(int i = 0; i < adj.size(); i++) {
				for(int j = 0; j < adj.get(i).size(); j++) {
					int ID = adj.get(i).get(j).b;
					eds[ID] = new tup(i, adj.get(i).get(j).a, 0);
				}
			}
			
			for(tup each: eds) {
				out.println(each);
			}
		}
		
		public static void dfs(int node, int timeElapsed) {
			
		}
		
		static int[] bestTime;
	}
	static long binpow(long a, long b, long m) {
		a %= m;
		long res = 1;
		while (b > 0) {
			if ((b & 1) == 1)
				res = res * a % m;
			a = a * a % m;
			b >>= 1;
		}
		return res;
	}
	static void sort(int[] x){
		shuffle(x);
		Arrays.sort(x);
	}
	static void sort(long[] x){
		shuffle(x);
		Arrays.sort(x);
	}
	static class tup implements Comparable<tup>, Comparator<tup>{
		int a, b, id;
		tup(int a,int b, int id){
			this.a=a;
			this.b=b;
			this.id = id;
		}
		public tup() {
		}
		@Override
		public int compareTo(tup o){
			if(b == o.b)
				return Integer.compare(o.id, id);
			return Integer.compare(b,o.b);
		}
		@Override
		public int compare(tup o1, tup o2) {
			if(o1.b == o2.b)
				return Integer.compare(o2.id, o1.id);
			return Integer.compare(o1.b, o2.b);
		}
		
		@Override
	    public int hashCode() {
			return Objects.hash(a, b);
	    }
 
	    @Override
	    public boolean equals(Object obj) {
	    	if (this == obj)
                return true;
	    	if (obj == null)
                return false;
	    	if (getClass() != obj.getClass())
                return false;
	    	tup other = (tup) obj;
	    	return a==other.a && b==other.b;
	    }
	    
	    @Override
	    public String toString() {
	    	return a + " " + b;
	    }
	}
	
	static void shuffle(int[] a) {
		Random get = new Random();
		for (int i = 0; i < a.length; i++) {
			int r = get.nextInt(a.length);
			int temp = a[i];
			a[i] = a[r];
			a[r] = temp;
		}
	}

	static void shuffle(long[] a) {
		Random get = new Random();
		for (int i = 0; i < a.length; i++) {
			int r = get.nextInt(a.length);
			long temp = a[i];
			a[i] = a[r];
			a[r] = temp;
		}
	}

	static class FastReader {
		BufferedReader br;
		StringTokenizer st;

		public FastReader() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		public FastReader(String s) throws FileNotFoundException {
			br = new BufferedReader(new FileReader(new File(s)));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}
	}

}