#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using VI = vector<int>;
using VL = vector<ll>;
using loop = int;
template<class T> using PQ = priority_queue<T, vector<T>, greater<T>>;
#define FOR(i,a,n) for(loop (i)=(a);(i)<(n);++(i))
#define eFOR(i,a,n) for(loop (i)=(a);(i)<=(n);++(i))
#define rFOR(i,a,n) for(loop (i)=(n)-1;(i)>=(a);--(i))
#define erFOR(i,a,n) for(loop (i)=(n);(i)>=(a);--(i))
#define each(i, a) for(auto &i : a)
#define SORT(i) sort((i).begin(),(i).end())
#define rSORT(i,a) sort((i).begin(),(i).end(),(a))
#define all(i) (i).begin(),(i).end()
#define out(y,x) ((y) < 0 || h <= (y) || (x) < 0 || w <= (x))
#define line cout << "------------------------\n" 
#define ENDL(i,n) ((i) == (n) - 1 ? "\n" : " ")
#define stop system("pause") //comment out this on AOJ.
constexpr ll INF = 1000000000;
constexpr ll LLINF = 1LL << 60;
constexpr ll mod = 1000000007;
constexpr ll MOD = 998244353;
constexpr ld eps = 1e-10;
constexpr ld pi = 3.1415926535897932;
template<class T>inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; }return false; }
template<class T>inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; }return false; }
inline void init() { cin.tie(nullptr); cout.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); }
template<class T>inline istream& operator>>(istream& is, vector<T>& v) { for (auto& elemnt : v)is >> elemnt; return is; }
template<class T, class U>inline istream& operator>>(istream& is, pair<T, U>& p) { is >> p.first >> p.second; return is; }
template<class T>inline vector<T> vec(size_t a) { return vector<T>(a); }
template<class T>inline vector<T> defvec(T def, size_t a) { return vector<T>(a, def); }
template<class T, class... Ts>inline auto vec(size_t a, Ts... ts) { return vector<decltype(vec<T>(ts...))>(a, vec<T>(ts...)); }
template<class T, class... Ts>inline auto defvec(T def, size_t a, Ts... ts) { return vector<decltype(defvec<T>(def, ts...))>(a, defvec<T>(def, ts...)); }

int main() {
    init();

    int n, m; cin >> n >> m;
    deque<int> ans;
    vector<bool> used(n);
    vector<set<int>> g(n);
    FOR(i, 0, m) {
        int a, b; cin >> a >> b;
        --a, --b;
        if (i == 0) {
            ans.push_back(a);
            ans.push_back(b);
            used[a] = true;
            used[b] = true;
        }
        g[a].insert(b);
        g[b].insert(a);
    }

    function<bool()> check = [&]() {
        {
            auto itr = g[ans.front()].begin();
            for (; itr != g[ans.front()].end(); ++itr) {
                if (!used[*itr]) {
                    used[*itr] = true;
                    ans.push_front(*itr);
                    return false;
                }
            }
        }
        {
            auto itr = g[ans.back()].begin();
            for (; itr != g[ans.back()].end(); ++itr) {
                if (!used[*itr]) {
                    used[*itr] = true;
                    ans.push_back(*itr);
                    return false;
                }
            }
        }
        return true;
    };

    while (!check());
    cout << ans.size() << "\n";
    FOR(i, 0, ans.size())cout << ans[i] + 1 << ENDL(i, ans.size());
}

Measured memory_bytes: 15360