#include <bits/stdc++.h>
#define int long long
#define ll long long
using ull = unsigned long long;
using namespace std;
#define dump(x)                             \
    if (dbg) {                              \
        cerr << #x << " = " << (x) << endl; \
    }
#define overload4(_1, _2, _3, _4, name, ...) name
#define FOR1(n) for (ll i = 0; i < (n); ++i)
#define FOR2(i, n) for (ll i = 0; i < (n); ++i)
#define FOR3(i, a, b) for (ll i = (a); i < (b); ++i)
#define FOR4(i, a, b, c) for (ll i = (a); i < (b); i += (c))
#define FOR(...) overload4(__VA_ARGS__, FOR4, FOR3, FOR2, FOR1)(__VA_ARGS__)
#define FORR(i, a, b) for (int i = (a); i <= (b); ++i)
#define bit(n, k) ((n >> k) & 1) /*nのk bit目*/
namespace mydef {
const int INF = 1ll << 60;
const int MOD = 1e9 + 7;
template <class T>
bool chmin(T& a, const T& b) {
    if (a > b) {
        a = b;
        return 1;
    } else
        return 0;
}
template <class T>
bool chmax(T& a, const T& b) {
    if (a < b) {
        a = b;
        return 1;
    } else
        return 0;
}
void Yes(bool flag = true) {
    if (flag)
        cout << "Yes" << endl;
    else
        cout << "No" << endl;
}
void No(bool flag = true) {
    Yes(!flag);
}
void YES(bool flag = true) {
    if (flag)
        cout << "YES" << endl;
    else
        cout << "NO" << endl;
}
void NO(bool flag = true) {
    YES(!flag);
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T& val) {
    std::fill((T*)array, (T*)(array + N), val);
}
bool dbg = false;
}  // namespace mydef
using namespace mydef;
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
#define all(v) (v).begin(), (v).end()
#define SZ(x) ((int)(x).size())
#define vi vector<int>
#define vvi vector<vector<int>>
#define vp vector<pair<int, int>>
#define vvp vector<vector<pair<int, int>>>
#define pi pair<int, int>
//#define P pair<int, int>
//#define V vector<int>
//#define S set<int>
#define asn ans


class UnWeightedGraph : public vector<vector<int>> {
private:
    int M;  //M:辺の数
    bool undirected = false;
    bool directed = false;
    //
public:
    UnWeightedGraph() = default;
    void build_undirected(int m) {
        assert(!(*this).empty());
        assert(!directed);
        undirected = true;
        M = m;
        while (m--) {
            int a, b;
            cin >> a >> b;
            a--;
            b--;
            (*this)[a].emplace_back(b);
            (*this)[b].emplace_back(a);
        }
    }
    void build_undirected(int n, int m) {
        (*this).resize(n);
        build_undirected(m);
    }
    void build_directed(int m) {
        assert(!(*this).empty());
        assert(!undirected);
        directed = true;
        M = m;
        while (m--) {
            int a, b;
            cin >> a >> b;
            a--;
            b--;
            (*this)[a].emplace_back(b);
        }
    }
    void build_directed(int n, int m) {
        (*this).resize(n);
        build_undirected(m);
    }
};
//グローバルでの使用のみ想定

int N, M;
UnWeightedGraph G;

vi ans;
int used[202020];

void f(int x) {
    if (!used[x])
        ans.emplace_back(x);
    used[x] = 1;
    for (auto& nxt : G[x]) {
        if (!used[nxt]) {
            f(nxt);
            return;
        }
    }
}

void solve() {
    G.build_undirected(N, M);
    f(0);
    reverse(all(ans));
    f(0);
    cout << ans.size() << endl;
    for (auto& x : ans)
        cout << x + 1 << " ";
    cout << endl;
}

signed main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    cin >> N >> M;

    solve();
    return 0;
}


Measured memory_bytes: 13288