//
//  main.cpp
//  2.C
//
//  Created by Andrey Chulkov on 7/29/15.
//  Copyright (c) 2015 Andrey Chulkov. All rights reserved.
//

#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <algorithm>

#define m_p make_pair

using namespace std;
typedef pair<int, int> int_pair;
int t = 0;
vector<int> tin;
vector<int> tout;
vector<bool> used;
vector<vector<int_pair>> graph;
vector<int> bridges;
map<pair<int, int>, int> edge_id;
const int N = 1e5 + 7;

int dfs_fup(int v, int from) {
    int fup;
    used[v] = true;
    tin[v] = t;
    fup = tin[v];
    t += 1;
    for (auto u : graph[v]) {
        if (!used[u.first] && (u.second != from)) {
            int fup_u;
            fup_u = dfs_fup(u.first, u.second);
            fup = min(fup_u, fup);
            if (tin[v] < fup_u) {
                cout << v << " " << u.first << endl;
                bridges.push_back(edge_id[make_pair(v, u.first)]);
            }
        }
        else if (u.second != from) {
            fup = min(tin[u.first], fup);
        }
    }
    tout[v] = t;
    t += 1;
    return fup;
}

int main() {
    int n, m;
    cin >> n >> m;
    graph.assign(n, vector<int_pair>());
    used.assign(n, false);
    tin.resize(n);
    tout.resize(n);
    for (int i = 0; i < m; i ++) {
        int b_i, e_i;
        cin >> b_i >> e_i;
        graph[b_i - 1].push_back(m_p(e_i - 1, i));
        graph[e_i - 1].push_back(m_p(b_i - 1, i));
        edge_id[m_p(b_i - 1, e_i - 1)] = i + 1;
        edge_id[m_p(e_i - 1, b_i - 1)] = i + 1;
    }
    for (int v = 0; v < n; v ++) {
        if (!used[v]) {
            dfs_fup(v, N);
        }
    }
    int k;
    k = (int) bridges.size();
    cout << k << endl;
    sort(bridges.begin(), bridges.end());
    for (int i = 0; i < k; i ++) {
        cout << bridges[i] << endl;
    }
    return 0;
}