E

#include <algorithm>
#include <iostream>
#include <iomanip>
#include <vector>
#include <array>
#include <set>
#include <map>

using namespace std;

#define int long long

//const long long INF = 1e18 + 7;
const int MAXN = 1e5 + 100;
//const int N = 1e5 + 10;
//const int MOD = 1e9 + 7;

int dp[MAXN][2];
vector<vector<int>> g;
map<pair<int, int>, pair<int, int>> edges;
map<pair<int, int>, int> pos;

void dfs(int v, int p) {
    dp[v][0] = dp[v][1] = 0;
    for (auto to: g[v]) {
        if (to == p) continue;
        dfs(to, v);
        dp[v][0] = max(max(dp[v][0], dp[to][0]), dp[to][1]);
        dp[v][1] = max(dp[v][1], dp[to][0]);
    }
    ++dp[v][1];
}

vector<pair<int, pair<int, int>>> ans;

void get_ans(int v, int p = -1) {
    for (auto to: g[v]) {
        if (to == p) continue;
        if (dp[to][1] > dp[to][0]) {
            int x = min(v + 1, to + 1), y = max(v + 1, to + 1);
            int x1 = edges[make_pair(x, y)].first, y1 = edges[make_pair(x, y)].second;
            ans.emplace_back(make_pair(pos[make_pair(x1, y1)], make_pair(x1, y1)));
        }
        get_ans(to, v);
    }
}

bool comp(const pair<int, pair<int, int>>& lhs, const pair<int, pair<int, int>>& rhs) {
    return lhs.first < rhs.first;
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int n, m;
    cin >> n >> m;
    g.resize(n);
    for (int i = 0; i < m; ++i) {
        int u, v;
        cin >> u >> v;
        pair<int, int> tmp = make_pair(min(u, v), max(u, v));
        edges[tmp] = make_pair(u, v);
        pos[tmp] = i;
        --u, --v;
        g[u].emplace_back(v);
        g[v].emplace_back(u);
    }

    dfs(0, -1);

    ans.reserve(m);
    get_ans(0);
    cout << ans.size() << '\n';
    sort(ans.begin(), ans.end(), comp);
    for (int i = 0; i < (int)ans.size(); ++i) {
        cout << ans[i].second.first << ' ' << ans[i].second.second << '\n';
    }
}