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:

/**
 *
 * @author meashish
 */
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStreamWriter;
import java.io.PrintStream;
import java.io.Serializable;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.HashMap;
import java.util.InputMismatchException;

public class Main {

    InputReader in;
    Printer out;

    long MOD = 1000000007;

    private void start() throws Exception {
        int n = in.nextInt();
        int m = in.nextInt();

        Edge edges[] = new Edge[m];
        HashMap<Pair<Integer, Integer>, Edge> map = new HashMap<>();

        int wt[] = new int[m];
        int incl[] = new int[m];

        for (int i = 0; i < m; i++) {
            wt[i] = in.nextInt();
            incl[i] = in.nextInt();
        }

        int a = 1, b = 2;
        for (int i = 0; i < m; i++) {
            if (incl[i] == 0) {
                continue;
            }
            edges[i] = new Edge(a, b, wt[i], incl[i] == 1);
            edges[i].index = i;

            //out.println("a b " + a + " " + b);
            b++;
            if (b > n) {
                a++;
                b = a + 1;
            }
        }
        for (int i = 0; i < m; i++) {
            if (incl[i] == 1) {
                continue;
            }
            edges[i] = new Edge(a, b, wt[i], incl[i] == 1);
            edges[i].index = i;
            //out.println("a b " + a + " " + b);
            b++;
            if (b > n) {
                a++;
                b = a + 1;
            }
        }

        Arrays.sort(edges, (Edge t, Edge t1) -> {
            Edge edge1 = t;
            Edge edge2 = t1;

            if (edge1.wt == edge2.wt) {
                if (edge1.included == true && edge2.included == true) {
                    return 0;
                }
                if (edge1.included == false && edge2.included == false) {
                    return 0;
                }
                if (edge1.included == true) {
                    return -1;
                } else {
                    return 1;
                }
            }

            return edge1.wt - edge2.wt;
        });
        boolean canbe = true;

        a = 1;
        b = 2;

        int curb = 2;
        int count[] = new int[100005];
        for (int i = 2; i <= n; i++) {
            count[i] = i;
        }

        for (Edge edge : edges) {
            if (!edge.included) {

                int initial = curb;
                //out.println("curb " + curb);
                while (count[curb] >= b - 1) {
                    curb++;

                    if (curb >= b - 1) {
                        curb = 2;
                    }

                    if (initial == curb) {
                        canbe = false;
                        break;
                    }
                }

                edge.e1 = curb;
                edge.e2 = count[curb] + 1;
                count[curb]++;
                curb++;

                if (curb >= b - 1) {
                    curb = 2;
                }

                continue;
            }

            edge.e1 = a;
            edge.e2 = b;

            b++;
        }

        Arrays.sort(edges, (Edge t, Edge t1) -> t.index - t1.index);
        //out.println(edges);
        if (!canbe) {
            out.println(-1);
        } else {
            a = 1;
            b = 1;
            for (int i = 0; i < m; i++) {
                out.println(edges[i].e1 + " " + edges[i].e2);
            }
        }
        out.flush();
    }

    class Edge {

        int index;
        int e1, e2;
        boolean included;
        int wt;

        public Edge(int a, int b, int wt, boolean bool) {
            this.e1 = a;
            this.e2 = b;
            this.wt = wt;
            this.included = bool;
        }

        @Override
        public String toString() {
            return e1 + "->" + e2 + " " + wt + " " + included + "\n";
        }
    }

    long power(long x, long n) {
        if (n <= 0) {
            return 1;
        }
        long y = power(x, n / 2);

        if ((n & 1) == 1) {
            return (((y * y) % MOD) * x) % MOD;
        }

        return (y * y) % MOD;
    }

    public int gcd(int a, int b) {
        a = Math.abs(a);
        b = Math.abs(b);
        return BigInteger.valueOf(a).gcd(BigInteger.valueOf(b)).intValue();
    }

    public static void main(String[] args) throws Exception {
        InputReader in;
        PrintStream out;

        //in = new InputReader(new FileInputStream(new File("in.txt")));
        //out = new PrintStream("out.txt");
        in = new InputReader(System.in);
        out = System.out;

        Main main = new Main();

        main.in = in;
        main.out = new Printer(out);

        main.start();
    }

    private static 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 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 - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public String nextString() {
            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 double nextDouble() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            double res = 0;
            while (!isSpaceChar(c) && c != '.') {
                if (c == 'e' || c == 'E') {
                    return res * Math.pow(10, nextInt());
                }
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read();
            }
            if (c == '.') {
                c = read();
                double m = 1;
                while (!isSpaceChar(c)) {
                    if (c == 'e' || c == 'E') {
                        return res * Math.pow(10, nextInt());
                    }
                    if (c < '0' || c > '9') {
                        throw new InputMismatchException();
                    }
                    m /= 10;
                    res += (c - '0') * m;
                    c = read();
                }
            }
            return res * sgn;
        }

        public long nextLong() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long 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 c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public String next() {
            return nextString();
        }

        public interface SpaceCharFilter {

            public boolean isSpaceChar(int ch);
        }
    }

    private static class Printer {

        PrintStream out;
        StringBuilder buffer = new StringBuilder();
        boolean autoFlush;

        public Printer(PrintStream out) {
            this.out = out;
        }

        public Printer(PrintStream out, boolean autoFlush) {
            this.out = out;
            this.autoFlush = autoFlush;
        }

        public void println() {
            buffer.append("\n");

            if (autoFlush) {
                flush();
            }
        }

        public void println(int n) {
            println(Integer.toString(n));
        }

        public void println(long n) {
            println(Long.toString(n));
        }

        public void println(double n) {
            println(Double.toString(n));
        }

        public void println(float n) {
            println(Float.toString(n));
        }

        public void println(boolean n) {
            println(Boolean.toString(n));
        }

        public void println(char n) {
            println(Character.toString(n));
        }

        public void println(byte n) {
            println(Byte.toString(n));
        }

        public void println(short n) {
            println(Short.toString(n));
        }

        public void println(Object o) {
            println(o.toString());
        }

        public void println(Object[] o) {
            println(Arrays.deepToString(o));
        }

        public void println(String s) {
            buffer.append(s).append("\n");

            if (autoFlush) {
                flush();
            }
        }

        public void print(char s) {
            buffer.append(s);

            if (autoFlush) {
                flush();
            }
        }

        public void print(String s) {
            buffer.append(s);

            if (autoFlush) {
                flush();
            }
        }

        public void flush() {
            try {
                BufferedWriter log = new BufferedWriter(new OutputStreamWriter(out));
                log.write(buffer.toString());

                log.flush();
                buffer = new StringBuilder();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    private class Pair<T, U> implements Serializable {

        public long dist;
        int index;

        private T key;

        public T getKey() {
            return key;
        }

        private U value;

        public U getValue() {
            return value;
        }

        public Pair(T key, U value) {
            this.key = key;
            this.value = value;
        }

        @Override
        public String toString() {
            return key + "=" + value;
        }

        @Override
        public boolean equals(Object obj) {
            if (obj == null) {
                return false;
            }
            if (getClass() != obj.getClass()) {
                return false;
            }

            final Pair other = (Pair) obj;
            if (!this.key.equals(other.key)) {
                return false;
            }

            return this.value.equals(other.value);
        }

        @Override
        public int hashCode() {
            return key.hashCode() + 13 * value.hashCode();
        }
    }

    public class DisjointSets {

        private final int[] array;

        public DisjointSets(int numElements) {
            array = new int[numElements];
            for (int i = 0; i < array.length; i++) {
                array[i] = -1;
            }
        }

        public void union(int root1, int root2) {
            if (array[root2] < array[root1]) {
                array[root1] = root2;
            } else {
                if (array[root1] == array[root2]) {
                    array[root1]--;
                }
                array[root2] = root1;
            }
        }

        public int find(int x) {
            if (array[x] < 0) {
                return x;
            } else {
                array[x] = find(array[x]);
                return array[x];
            }
        }

        public void main(String[] args) {
            int NumElements = 128;
            int NumInSameSet = 16;

            DisjointSets s = new DisjointSets(NumElements);
            int set1, set2;

            for (int k = 1; k < NumInSameSet; k *= 2) {
                for (int j = 0; j + k < NumElements; j += 2 * k) {
                    set1 = s.find(j);
                    set2 = s.find(j + k);
                    s.union(set1, set2);
                }
            }

            for (int i = 0; i < NumElements; i++) {
                System.out.print(s.find(i) + "*");
                if (i % NumInSameSet == NumInSameSet - 1) {
                    System.out.println();
                }
            }
            System.out.println();
        }
    }
}