#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cctype>
#include <cassert>
#include <climits>
#include <string>
#include <bitset>
#include <cfloat>
#include <random>
#include <iomanip>
#include <unordered_set>
#pragma GCC optimize("Ofast")
using namespace std;
typedef long double ld;
typedef long long int ll;
typedef unsigned long long int ull;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef vector<pair<int,int> > vpii;
typedef vector<pair<ll,ll> > vpll;
typedef vector<vector<int> > vvi;
typedef vector<vector<char> > vvc;
typedef vector<vector<string> > vvs;
typedef vector<vector<ll> > vvll;
typedef map<int, int> mii;
typedef set<int> si;
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define irep(it, stl) for(auto it = stl.begin(); it != stl.end(); it++)
#define drep(i,n) for(int i = (n) - 1; i >= 0; --i)
#define fin(ans) cout << (ans) << '\n'
#define STLL(s) strtoll(s.c_str(), NULL, 10)
#define mp(p,q) make_pair(p, q)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define Sort(a) sort(a.begin(), a.end())
#define Rort(a) sort(a.rbegin(), a.rend())
#define MATHPI acos(-1)
#define itn int
// #define endl '\n';
#define fi first
#define se second
#define NONVOID [[nodiscard]]
const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
template <class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;} return 0;}
template <class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;} return 0;}
template <class T> inline void dump(T &v){irep(i, v){cout<<*i<<((i==--v.end())?'\n':' ');}}
inline string getline(){string s; getline(cin,s); return s;}
inline void yn(const bool b){b?fin("yes"):fin("no");}
inline void Yn(const bool b){b?fin("Yes"):fin("No");}
inline void YN(const bool b){b?fin("YES"):fin("NO");}
struct io{io(){ios::sync_with_stdio(false);cin.tie(0);}};
const int INF = INT_MAX;
const ll LLINF = 1LL<<60;
const ll MOD = 1000000007;
const double EPS = 1e-9;

class Bridge {
    int N, num = 0;
    vvi G;
    vi pre, low;
    vb isPassed;
    vpii bridges;

    int culcLow(const int v, const int bef) {
        int nowLow = num;
        low[v] = pre[v] = nowLow;
        for(auto ne : G[v]) {
            if(ne == bef) continue;
            if(ne == 0) {
                low[0] = -1;
            }
            if(pre[ne] == -1) {
                num++;
                culcLow(ne, v);
            }
            chmin(nowLow, low[ne]);
        }
        return low[v] = nowLow;
    }

    void traceGraph(const int v, const int bef) {
        for(auto ne : G[v]) {
            if(ne == bef) continue;
            if(!isPassed[ne]) {
                if(low[ne] == pre[ne]) {
                    bridges.emplace_back(min(v, ne), max(v, ne));
                }
                isPassed[ne] = true;
                traceGraph(ne, v);
            }
        }
    }

public:
    Bridge(const int _n, const vvi _G) : N(_n), G(_G) {
        pre = vi(N, -1);
        low = vi(N, INF);
        isPassed = vb(N, false);
        isPassed[0] = true;
    }

    void findBridges() {
        culcLow(0, -1);
        traceGraph(0, -1);
        Sort(bridges);
    }

    void show() {
        for(auto p : bridges) {
            cout << p.fi << " " << p.se << endl; 
        }
    }
};

int main() {

    int v, e;
    cin >> v >> e;
    vvi g(v);
    rep(i, e) {
        int s, t;
        cin >> s >> t;
        g[s].pb(t);
        g[t].pb(s);
    }
    Bridge bg(v, g);
    bg.findBridges();
    bg.show();
    
}




Measured memory_bytes: 5544