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.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.StringTokenizer;

/**
 * @author Don Li
 */
public class LazyStudent {

    int n, m;
    Edge[] edges;
    Pair[] res;

    void solve() {
        n = in.nextInt();
        m = in.nextInt();
        edges = new Edge[m];
        for (int i = 0; i < m; i++) {
            edges[i] = new Edge(i, in.nextInt(), in.nextInt());
        }

        // sort the edges by weight then by selected or not, according to Kruskal algorithm
        Arrays.sort(edges, (p, q) -> {
            if (p.w != q.w) return p.w - q.w;
            if (p.in && !q.in) return -1;
            if (!p.in && q.in) return 1;
            return p.id - q.id;
        });

        // build MST according to Kruskal algorithm, add tree edge as (0,1), (0,2) ... (0, n-1), cycle edge as (1,2), (1,3), (2,3), (1,4), (2,4), (3,4) ...
        res = new Pair[m];
        boolean ok = build();

        if (!ok) out.println(-1);
        else {
            for (int i = 0; i < m; i++) {
                out.printf("%d %d%n", res[i].u, res[i].v);
            }
        }
    }

    boolean build() {
        // the least weighted edges must be in the MST
        if (!edges[0].in) return false;
        assignEdge(edges[0].id, 0, 1);
        
        int cnt = 2;
        int p = 1, q = 2;

        for (int i = 1; i < m; i++) {
            Edge e = edges[i];
            if (e.in) {
                // always add tree edge to vertex 0 (in order to maximize the ways to add cycle edges)
                assignEdge(e.id, 0, cnt++);
            } else {
                // assign the cycle edge as (p,q)
                if (p == q) {
                    p = 1;
                    q++;
                }
                if (q >= cnt) return false;
                assignEdge(e.id, p++, q);
            }
        }

        return true;
    }

    void assignEdge(int i, int u, int v) {
        res[i] = new Pair(u + 1, v + 1);
    }

    static class Edge {
        int id;
        int w;
        boolean in;

        public Edge(int id, int w, int in) {
            this.id = id;
            this.w = w;
            this.in = in == 1;
        }
    }

    static class Pair {
        int u, v;

        public Pair(int u, int v) {
            this.u = u;
            this.v = v;
        }
    }

    public static void main(String[] args) {
        in = new FastScanner(new BufferedReader(new InputStreamReader(System.in)));
        out = new PrintWriter(System.out);
        new LazyStudent().solve();
        out.close();
    }

    static FastScanner in;
    static PrintWriter out;

    static class FastScanner {
        BufferedReader in;
        StringTokenizer st;

        public FastScanner(BufferedReader in) {
            this.in = in;
        }

        public String nextToken() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(in.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(nextToken());
        }

        public long nextLong() {
            return Long.parseLong(nextToken());
        }

        public double nextDouble() {
            return Double.parseDouble(nextToken());
        }
    }
}