// Copyright (C) 2017 __debug.

// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; version 3

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program; If not, see <http://www.gnu.org/licenses/>.


#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/priority_queue.hpp>

#define x first
#define y second
#define MP std::make_pair
#define SZ(x) ((int)(x).size())
#define ALL(x) (x).begin(), (x).end()
#define DEBUG(...) fprintf(stderr, __VA_ARGS__)
#ifdef __linux__
#define getchar getchar_unlocked
#define putchar putchar_unlocked
#endif

using std::pair;
using std::vector;
using std::string;

typedef long long LL;
typedef pair<int, int> Pii;

const int oo = 0x3f3f3f3f;

template<typename T> inline bool chkmax(T &a, T b) { return a < b ? a = b, true : false; }
template<typename T> inline bool chkmin(T &a, T b) { return b < a ? a = b, true : false; }
string procStatus()
{
    std::ifstream t("/proc/self/status");
    return string(std::istreambuf_iterator<char>(t), std::istreambuf_iterator<char>());
}
template<typename T> T read(T &x)
{
    int f = 1;
    char ch = getchar();
    for (; !isdigit(ch); ch = getchar())
        f = (ch == '-' ? -1 : 1);
    for (x = 0; isdigit(ch); ch = getchar())
        x = 10 * x + ch - '0';
    return x *= f;
}
template<typename T> void write(T x)
{
    if (x == 0) {
        putchar('0');
        return;
    }
    if (x < 0) {
        putchar('-');
        x = -x;
    }
    static char s[20];
    int top = 0;
    for (; x; x /= 10)
        s[++top] = x % 10 + '0';
    while (top)
        putchar(s[top--]);
}
// EOT

const int MAXN = 1e5 + 5, MAXM = 2e5 + 5;

struct Edge {
    int u, v, next;
    Edge() { }
    Edge(int u_, int v_, int next_): u(u_), v(v_), next(next_) { }
};

int N, M;
int tote, head[MAXN];
Edge edge[MAXM];

inline void addEdge(int u, int v)
{
    edge[++tote] = Edge(u, v, head[u]);
    head[u] = tote;
}

void input()
{
    read(N); read(M);
    for (int i = 1; i <= M; ++i) {
        int u, v;
        read(u); read(v);
        addEdge(u, v);
        addEdge(v, u);
    }
}

bool vis[MAXN];
std::list<int> ans;

void solve()
{
    int s = edge[1].u, t = edge[1].v;
    // printf("%d %d\n", s, t);
    while (!vis[s] || !vis[t]) {
        if (!vis[s]) ans.push_front(s);
        if (!vis[t]) ans.push_back(t);
        vis[s] = vis[t] = true;
        for (int i = head[s]; i; i = edge[i].next) {
            int v = edge[i].v;
            if (!vis[v]) {
                s = v;
                break;
            }
        }
        for (int i = head[t]; i; i = edge[i].next) {
            int v = edge[i].v;
            if (!vis[v] && v != s) {
                t = v;
                break;
            }
        }
    }

    printf("%d\n", SZ(ans));
    for (auto x : ans) {
        printf("%d ", x);
    }
    puts("");
}

int main()
{
#ifdef __DEBUG
    freopen("B.in", "r", stdin);
    freopen("B.out", "w", stdout);
#endif

    input();
    solve();

    return 0;
}

// 男儿何不带吴钩，收取关山五十州。
//     -- 李贺《南园十三首·其五》


Measured memory_bytes: 6528