#include "bits/stdc++.h"

using namespace std;
using lint = int64_t;

int main(void) {
    cin.tie(nullptr)->sync_with_stdio(false);
    int n, m;
    cin>>n>>m;
    vector<vector<pair<int, int>>>g(n);
    vector<pair<int, int>>e(m);
    for(int i=0;i<m;i++){
        int a, b;
        cin>>a>>b;
        a--, b--;
        g[a].emplace_back(b, i);
        g[b].emplace_back(a, i);
        e[i] = {a, b};
    }
    vector<int>h(n), dp(n);
    vector<bool>vis(n), w(m);
    bool is_tree = true;
    auto dfs = [&](auto& self, int u)->void {
        vis[u] = 1;
        for(auto [v, ind] : g[u]){
            if(!vis[v]){
                h[v] = h[u] + 1;
                self(self, v);
                dp[u] += dp[v];
                if(!dp[v]) w[ind] = 1;
                else is_tree = false;
            } 
            else{
                if(h[v] > h[u] + 1) dp[u]--;
                if(h[v] < h[u] - 1) dp[u]++;
            }
        }
    };
    vector<bool>tree(n);
    auto comp_tree = [&](auto& self, int u)->void {
        tree[u] = 1;
        for(auto [v, ind] : g[u]){
            if(tree[v]) continue;
            self(self, v);
        }
    };
    for(int i=0;i<n;i++) if(!vis[i]){
        dfs(dfs, i);
        if(!is_tree){
            is_tree = true;
        }
        else{
            comp_tree(comp_tree, i);
        }
    }
    vector<int>color(n, -1);
    int cur = 0;
    auto dfs2 = [&](auto& self, int u)->void {
        color[u] = cur;
        for(auto [v, ind] : g[u]){
            if(color[v] != -1 || w[ind]) continue;
            self(self, v);
        }
    };
    for(int i=0;i<n;i++) if(color[i] == -1) dfs2(dfs2, i), cur++;
    vector<vector<pair<int, int>>>adj(cur);
    vector<int>cnt(cur);
    for(int i=0;i<n;i++) cnt[color[i]]++;
    vector<int>deg(cur);
    for(int i=0;i<m;i++){
        if(!w[i]) continue; 
        auto [a, b] = e[i];
        adj[color[a]].emplace_back(color[b], i);
        adj[color[b]].emplace_back(color[a], i);
    }
    vector<int>dp2(cur);
    for(int i=0;i<cur;i++) if(cnt[i] > 1) dp2[i] = 1;
    vector<bool>vis2(cur);
    vector<pair<int, int>>ans;

    auto dfs3 = [&](auto& self, int u, int p)->void {
        vis2[u] = 1;
        for(auto [v, ind] : adj[u]){
            if(v == p) continue;
            self(self, v, u);
            dp2[u] += dp2[v];
        }
        if(dp2[u]){
            for(auto [v, ind] : adj[u]){
                if(v == p) continue;
                if(!dp2[v]){
                    auto [a, b] = e[ind];
                    if(color[a] != u) swap(a, b);
                    ans.emplace_back(a, b);
                }
            }
        }
    };
    for(int i=0;i<cur;i++){
        if(dp2[i] && !vis2[i]){
            dfs3(dfs3, i, i);
        }
    }
    for(int i=0;i<n;i++){
        if(tree[i] && g[i].size() == 1){
            auto [j, ind] = g[i][0];
            ans.emplace_back(i, j);
        }
    }
    sort(ans.begin(), ans.end());
    cout<<ans.size()<<"\n";
    for(auto [a, b] : ans) cout<<a+1<<" "<<b+1<<"\n";




    return 0;
}