using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Collections.Generic;
using System.Diagnostics;
using Enu = System.Linq.Enumerable;

public class Program
{
    public void Solve()
    {
        int N = Reader.Int(), M = Reader.Int();
        var E = Reader.IntTable(M);
        var bridges = new TwoEdgeConnectedComponent(N, E).Bridges;
        Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
        bridges.ForEach(b => Console.WriteLine(b[0] + " " + b[1]));
        Console.Out.Flush();
        Console.ReadLine();
    }
}

public class TwoEdgeConnectedComponent
{
    int N, id;
    List<int>[] E;
    int[] component, order;
    bool[] inS;
    Stack<int> S = new Stack<int>(), roots = new Stack<int>();
    List<int[]> vertexes = new List<int[]>();
    HashSet<long> BridgesSet = new HashSet<long>();
    public List<int[]> Bridges = new List<int[]>();

    public TwoEdgeConnectedComponent(int N) { Init(N); }
    public TwoEdgeConnectedComponent(int N, int[][] E, int origin = 0)
    {
        Init(N);
        Array.ForEach(E, e => AddEdge(e[0] - origin, e[1] - origin));
        Decompose();
    }

    void Init(int N)
    {
        this.N = N;
        component = new int[N];
        order = new int[N];
        inS = new bool[N];
        E = new List<int>[N];
        for (int i = 0; i < N; i++) E[i] = new List<int>();
    }

    public void AddEdge(int a, int b)
    {
        E[a].Add(b);
        E[b].Add(a);
    }

    public void Decompose()
    {
        for (int i = 0; i < N; i++)
            if (order[i] == 0)
                DFS(i, -1);
        Bridges.Sort((a, b) => a[0] != b[0] ? a[0] - b[0] : a[1] - b[1]);
    }

    void DFS(int v, int prev)
    {
        order[v] = ++id;
        roots.Push(v);
        S.Push(v);
        inS[v] = true;
        foreach (int next in E[v])
            if (order[next] == 0)
                DFS(next, v);
            else if (next != prev && inS[next])
                while (order[roots.Peek()] > order[next]) roots.Pop();
        if (roots.Peek() != v) return;
        if (prev != -1) AddBridge(prev, v);
        AddComponent(v);
    }

    void AddBridge(int a, int b)
    {
        BridgesSet.Add(ToKey(a, b));
        Bridges.Add(new[] { Math.Min(a, b), Math.Max(a, b) });
    }

    void AddComponent(int root)
    {
        int compId = vertexes.Count;
        var vs = new List<int>();
        for (; ; )
        {
            int v = S.Pop();
            inS[v] = false;
            component[v] = compId;
            vs.Add(v);
            if (v == root) break;
        }
        vertexes.Add(vs.ToArray());
        roots.Pop();
    }


    long ToKey(long a, long b) { return a < b ? a * N + b : b * N + a; }

}

class Entry { static void Main() { new Program().Solve(); } }
class Reader
{
    static TextReader reader = Console.In;
    static readonly char[] separator = { ' ' };
    static readonly StringSplitOptions op = StringSplitOptions.RemoveEmptyEntries;
    static string[] A = new string[0];
    static int i;
    static void Init() { Dispose(); A = new string[0]; }
    public static void Set(TextReader r) { Init(); reader = r; }
    public static void Set(string file) { Init(); reader = new StreamReader(file); }
    public static bool HasNext() { return CheckNext(); }
    public static string String() { return Next(); }
    public static int Int() { return int.Parse(Next()); }
    public static long Long() { return long.Parse(Next()); }
    public static double Double() { return double.Parse(Next()); }
    public static int[] IntLine() { return Array.ConvertAll(Split(Line()), int.Parse); }
    public static int[] IntArray(int N) { return Range(N, Int); }
    public static int[][] IntTable(int H) { return Range(H, IntLine); }
    public static string[] StringArray(int N) { return Range(N, Next); }
    public static string[][] StringTable(int N) { return Range(N, () => Split(Line())); }
    public static string Line() { return reader.ReadLine().Trim(); }
    public static T[] Range<T>(int N, Func<T> f) { var r = new T[N]; for (int i = 0; i < N; r[i++] = f()) ; return r; }
    public static void Dispose() { reader.Dispose(); }
    static string[] Split(string s) { return s.Split(separator, op); }
    static string Next() { CheckNext(); return A[i++]; }
    static bool CheckNext()
    {
        if (i < A.Length) return true;
        string line = reader.ReadLine();
        if (line == null) return false;
        if (line == "") return CheckNext();
        A = Split(line);
        i = 0;
        return true;
    }
}

Measured memory_bytes: 17252