#include <algorithm>
#include <iostream>
#include <fstream>
#include <vector>
#include <bitset>
using namespace std;
ifstream in("mesaj4.in");
ofstream out("mesaj4.out");
const int maxn = 100005;
bitset <maxn> viz;
vector <pair <int, int> > ans;
vector <int> vec[maxn];

void dfs(int nod)
{
    for(auto it : vec[nod])
    {
        if(!viz[it])
        {
            viz[it] = 1;
            dfs(it);
            ans.push_back(make_pair(nod, it));
        }
    }
}

int main()
{
    int n, m;
    in >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y;
        in >> x >> y;
        vec[x].push_back(y);
        vec[y].push_back(x);
    }
    viz[1] = 1;
    dfs(1);
    out << (n - 1) * 2 << "\n";
    for(auto it : ans)
        out << it.first << " " << it.second << "\n";
    reverse(ans.begin(), ans.end());
    for(auto it : ans)
        out << it.second << " " << it.first << "\n";
    return 0;
}