#include <iostream>
#include <string>
#include <vector>
#include <set>
#include <stack>
#include <queue>
#include <map>
#include <algorithm>
#include <iomanip>
#include <math.h>
#include <string.h>
#include <cstdio>
#include <tuple>
using namespace std; using ll = long long; using ld = long double;  using pll = pair<ll, ll>;
using vl = vector<ll>; using vll = vector<vl>; using vpll = vector<pll>;
const ld PI = 3.1415926535897932;
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#define rep1(n) for(ll i=0;i<n;++i)
#define rep2(i,n) for(ll i=0;i<n;++i)
#define rep3(i,a,b) for(ll i=a;i<b;++i)
#define rep4(i,a,b,c) for(ll i=a;i<b;i+=c)
#define rep(...) overload4(__VA_ARGS__,rep4,rep3,rep2,rep1)(__VA_ARGS__)
#define mp make_pair
#define mt make_tuple
#define INT(...) int __VA_ARGS__;in(__VA_ARGS__)
#define LL(...) ll __VA_ARGS__;in(__VA_ARGS__)
#define ULL(...) ull __VA_ARGS__;in(__VA_ARGS__)
#define STR(...) string __VA_ARGS__;in(__VA_ARGS__)
#define CHR(...) char __VA_ARGS__;in(__VA_ARGS__)
#define DBL(...) double __VA_ARGS__;in(__VA_ARGS__)
#define LD(...) ld __VA_ARGS__;in(__VA_ARGS__)
void in() {}
void debug_out() { cerr << endl; }
template<typename Head, typename... Tail>
void debug_out(Head h, Tail... t) {
	cerr << " " << h;
	if (sizeof...(t) > 0) cerr << " :";
	debug_out(t...);
}
template <typename T>
ostream& operator<<(ostream& os, vector<T> vec) {
	for (size_t i = 0; i < vec.size(); i++)os << vec[i] << (i + 1 == vec.size() ? "" : " ");
	return os;
}
ll ctoi(char c) {
	switch (c) {
	case '0': return 0; case '1': return 1; case '2': return 2;
	case '3': return 3; case '4': return 4; case '5': return 5;
	case '6': return 6; case '7': return 7; case '8': return 8;
	case '9': return 9;  default: return 0;
	}
}
bool pairCompare(const pll firstElof, pll secondElof)
{
	return firstElof.first > secondElof.first;
}
//**Snippetリスト**//
//rep, vin, all, iteLoop, bitSearch, bitList, nod//
//gcdlcm, isPrime, eratos, primeFactorize, Npow, combination, divisor, modinv,  digitDP//
//dfs, bfs, dijkstra, WarshallFloyd, BellmanFord, UnionFind, Kruskal ,RMQ, LCA//
ll i, j, k, l; ll N, M, K, H, W, L, X, Y, Z, R, Q;
ll MOD = 1000000007; ll INF = 1LL << 60; ll ans = 0; ll z = 0, o = 1;
vl flag; vll D; vll path; vector<string> A; ll magic = 0; vpll list;
//***********//
int main() {
	cin >> N >> M;
	path.resize(N);
	flag.resize(N);
	for (i = 0; i < M; i++) {
		ll a, b;
		cin >> a >> b;
		a--; b--;
		path[a].push_back(b);
		path[b].push_back(a);
	}
	vl L, R;
	L.push_back(0);
	R.push_back(path[0][0]);
	flag[0] = 1;
	flag[path[0][0]] = 1;
	ll left = 0;
	ll right = path[0][0];
	while (true) {
		ll newleft = -1;
		for (i = 0; i < path[left].size(); i++) {
			if (!flag[path[left][i]]) {
				L.push_back(path[left][i]);
				flag[path[left][i]] = 1;
				newleft = path[left][i];
				break;
			}
		}
		if (newleft == -1) break;
		left = newleft;
	}
	while (true) {
		ll newright = -1;
		for (i = 0; i < path[right].size(); i++) {
			if (!flag[path[right][i]]) {
				R.push_back(path[right][i]);
				flag[path[right][i]] = 1;
				newright = path[right][i];
				break;
			}
		}
		if (newright == -1) break;
		right = newright;
	}
	reverse(L.begin(), L.end());
	cout << L.size()+R.size() << endl;
	ll now = left;
	for (i = 0; i < L.size(); i++) {
		cout << L[i]+1 << " ";
	}
	for (i = 0; i < R.size(); i++) {
		cout << R[i]+1 << " ";
	}
}

Measured memory_bytes: 7924