#include <iostream>
#include <iomanip>
#include <cstdio>
#include <string>
#include <cstring>
#include <deque>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <utility>
#include <algorithm>
#include <map>
#include <set>
#include <complex>
#include <cmath>
#include <limits>
#include <climits>
#include <ctime>
#include <cassert>
using namespace std;

#define rep(i,a,n) for(int (i)=(a); (i)<(n); (i)++)
#define repq(i,a,n) for(int (i)=(a); (i)<=(n); (i)++)
#define repr(i,a,n) for(int (i)=(a); (i)>=(n); (i)--)
#define all(v) begin(v), end(v)
#define pb(a) push_back(a)
#define fr first
#define sc second
#define INF 2000000000
#define int long long int

#define X real()
#define Y imag()
#define EPS (1e-10)
#define EQ(a,b) (abs((a) - (b)) < EPS)
#define EQV(a,b) ( EQ((a).X, (b).X) && EQ((a).Y, (b).Y) )
#define LE(n, m) ((n) < (m) + EPS)
#define LEQ(n, m) ((n) <= (m) + EPS)
#define GE(n, m) ((n) + EPS > (m))
#define GEQ(n, m) ((n) + EPS >= (m))

typedef vector<int> VI;
typedef vector<VI> MAT;
typedef pair<int, int> pii;
typedef long long ll;

typedef complex<double> P;
typedef pair<P, P> L;
typedef pair<P, double> C;

int dy[]={0, 0, 1, -1};
int dx[]={1, -1, 0, 0};
int const MOD = 1000000007;

namespace std {
    bool operator<(const P& a, const P& b) {
        return a.X != b.X ? a.X < b.X : a.Y < b.Y;
    }
}

// ?§?????????¨????????¨???????????????????¨???????????§???????
struct Edge {
    int from, to, cost;
    Edge(int s, int d) : to(s), cost(d) {}
    Edge(int f, int s, int d) : from(f), to(s), cost(d) {}

    bool operator<(const Edge &e) const {
        return cost < e.cost;
    }
    bool operator>(const Edge &e) const {
        return cost > e.cost;
    }
};

// 1??????????????????????????????????????±????????????????????????????????? vector
// Edges????????????????????????????????????????????°??????????????????
typedef vector<Edge> Edges;

// ???????????±??????????????? vector
// Graph??????????????????????????°?????????????????§??? V ??§?????????
typedef vector<Edges> Graph;

struct graphLink {
    vector<bool> isthrough;
    vector<int> ord, low, parent;
    Graph G;
    int cnt, v;

    // init
    graphLink(int _n) : isthrough(_n, false), ord(_n, 0), low(_n, 0), parent(_n, 0), G(_n), cnt(0), v(_n) {}

    // example: dfs(0, -1);
    void dfs(int cur, int prev) {
        low[cur] = cnt;
        ord[cur] = cnt++;
        isthrough[cur] = true;

        for(auto x : G[cur]) {
            if(!isthrough[x.to]) {
                parent[x.to] = cur;
                dfs(x.to, cur);

                low[cur] = min(low[cur], low[x.to]);
            }
            else if(x.to != prev) {
                low[cur] = min(low[cur], ord[x.to]);
            }
        }
    }
    set<int> artPoints() {
        set<int> se;
        int num = 0;
        rep(i,0,v) {
            // printf("%lld: %lld %lld\n", i, ord[parent[i]], low[i]);
            if(parent[i] == 0) num++;
            else if(ord[parent[i]] <= low[i]) se.insert(parent[i]);
        }
        if(num > 2) se.insert(0);
        return se;
    }

    set<pii> bridges(vector<pii> vp) {
        set<pii> se;
        rep(i,0,vp.size()) {
            if(ord[vp[i].fr] < low[vp[i].sc] || ord[vp[i].sc] < low[vp[i].fr]) {
                // se.insert(vp[i]);
                int mi = min(vp[i].fr, vp[i].sc);
                int ma = max(vp[i].fr, vp[i].sc);
                se.insert(pii(mi, ma));
            }
        }
        return se;
    }
};

signed main() {
    int v, e; cin >> v >> e;
    graphLink gr(v);
    vector<pii> vp;

    int s, t;
    rep(i,0,e) {
        cin >> s >> t;
        gr.G[s].pb(Edge(t,1));
        gr.G[t].pb(Edge(s,1));
        vp.pb(pii(s, t));
    }
    gr.dfs(0, -1);

    // set<int> ret = gr.artPoints();
    set<pii> ret2 = gr.bridges(vp);
    // for(auto x : ret) cout << x << endl;
    for(auto x : ret2) printf("%lld %lld\n", x.fr, x.sc);
    return 0;
}

Measured memory_bytes: 8696