// 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》