#include <bits/stdc++.h>
#define N 100005

using namespace std;

ifstream fin ("euler.in");
ofstream fout ("euler.out");

int n, x, y, m;
list <int> L[N];
vector <int> ciclu;

void Euler(int nod)
{
    while (!L[nod].empty())
    {
        int nod2 = L[nod].front();

        L[nod].pop_front();
        L[nod2].erase(find(L[nod2].begin(), L[nod2].end(), nod));

        Euler(nod2);
    }
    ciclu.push_back(nod);
}

int main()
{
    fin >> n >> m;
    while (m--)
    {
        fin >> x >> y;
        L[x].push_back(y);
        L[y].push_back(x);
    }
    Euler(1);
    fout << ciclu.size() << "\n";
    for (auto &it : ciclu)
        fout << it << " ";
    return 0;
}