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//#pragma optimization_level 3
 
//#pragma comment(linker, "/stack:200000000")
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
 
#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <chrono>
#include <ctime>
#include <queue>
#include <math.h>
#include <deque>
#include <stack>
#include <iomanip>
#include <assert.h>
#include <stdio.h>
#include <cstring>
#include <random>
 
using namespace std;
 
#define int long long
#define ld long double
#define ull unsigned long long
#define endl '\n'
#define try tr
#define pii pair<int, int>
#define ti tuple <int, int, int>
#define vi vector <int>
#define vpi vector <pii>
#define umap unordered_map
#define uset unordered_set
#define left left11
#define right right11
#define all(c) (c).begin(), (c).end()
#define pb push_back
#define sqr(a) ((a) * (a))
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
 
#define X first
#define Y second
 
ld TL = 1.0;
bool is_tl = 0;
int CALLS = 0;
 
inline bool IS() {
    if (++CALLS == 1000) {
        CALLS = 0;
        is_tl |= clock() > (TL - 0.1) * CLOCKS_PER_SEC;
    }
    return is_tl;
}
 
template<typename T1, typename T2>
inline void amin(T1 &a, T2 b) { if (a > b) a = b; }
 
template<typename T1, typename T2>
inline void amax(T1 &a, T2 b) { if (a < b) a = b; }
 
template<typename T1, typename T2>
ostream &operator<<(ostream &os, pair<T1, T2> &p) {
    os << p.first << ' ' << p.second << endl;
    return os;
}
 
template<typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
    is >> p.first >> p.second;
    return is;
}
 
template<typename T>
ostream &operator<<(ostream &os, vector<T> &v) {
    for (auto &u : v) os << u << ' ';
    os << endl;
    return os;
}
 
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
const int N = 2e6 + 7, NS = 2e3 + 7, lg = 19, sq = 550, inf = 2e9 + 7, SM = 1e2 + 7;
const ld eps = 1e-9;
int hash_mod[4] = {1000000007, 998244353, 1000000009, 999999937}, mod = hash_mod[rnd() % 4];
int hash_pows[4] = {179, 239, 1007, 2003}, P = hash_pows[rnd() % 4];

void solve() {
	int n, m;
	cin >> n >> m;
	vector <vi> v(n);
	vi used(n);
	used[0] = 1;
	for (int i = 0; i < m; i++) {
		int a, b;
		cin >> a >> b;
		a--, b--;
		v[a].pb(b);
		v[b].pb(a);
	}
	deque <int> q;
	q.push_back(0);
	while(1) {
		int f = 0;
		for (auto u : v[q.front()]) {
			if(!used[u]) {
				q.push_front(u);
				used[u] = 1;
				f = 1;
				break;
			}
		}
		for (auto u : v[q.back()]) {
			if(!used[u]) {
				q.push_back(u);
				used[u] = 1;
				f = 1;
				break;
			}
		}
		if(!f)
			break;
	}
	cout << q.size() << endl;
	for (auto u : q)
		cout << u + 1 << ' ';
}
 
signed main() {
    fast
    solve();
}

Measured memory_bytes: 10168