#include <iostream>
#include <queue>
#include <map>
#include <list>
#include <vector>
#include <string>
#include <stack>
#include <limits>
#include <climits>
#include <cassert>
#include <fstream>
#include <cstring>
#include <cmath>
#include <bitset>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <cstdio>
#include <ciso646>
#include <set>
#include <array>
#include <unordered_map>

using namespace std;

#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)

#define inf 0x3f3f3f3f
#define PB push_back
#define MP make_pair
#define ALL(a) (a).begin(),(a).end()
#define SET(a,c) memset(a,c,sizeof a)
#define CLR(a) memset(a,0,sizeof a)
#define VS vector<string>
#define VI vector<ll>
#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define MIN(a,b) (a>b?b:a)
#define MAX(a,b) (a>b?a:b)
#define pi 2*acos(0.0)
#define INFILE() freopen("in0.txt","r",stdin)
#define OUTFILE()freopen("out0.txt","w",stdout)
#define ll long long
#define ull unsigned long long
#define pii pair<ll,ll>
#define pcc pair<char,char>
#define pic pair<ll,char>
#define pci pair<char,ll>
#define eps 1e-14
#define FST first
#define SEC second
#define SETUP cin.tie(0), ios::sync_with_stdio(false), cout << setprecision(15)

namespace {
	struct input_returnner {
		ll N; input_returnner(ll N_ = 0) :N(N_) {}
		template<typename T> operator vector<T>() const { vector<T> res(N); for (auto &a : res) cin >> a; return std::move(res); }
		template<typename T> operator T() const { T res; cin >> res; return res; }
		template<typename T> T operator - (T right) { return T(input_returnner()) - right; }
		template<typename T> T operator + (T right) { return T(input_returnner()) + right; }
		template<typename T> T operator * (T right) { return T(input_returnner()) * right; }
		template<typename T> T operator / (T right) { return T(input_returnner()) / right; }
		template<typename T> T operator << (T right) { return T(input_returnner()) << right; }
		template<typename T> T operator >> (T right) { return T(input_returnner()) >> right; }
	};
	template<typename T> input_returnner in() { return in<T>(); }
	input_returnner in() { return input_returnner(); }
	input_returnner in(ll N) { return std::move(input_returnner(N)); }
}

const ll MOD = 1e9 + 7;

struct ModInt {
	ll v = 0;
	ModInt() {}
	template<class T> ModInt(const T& right) {
		v = right;
		if (v >= 0) v %= MOD;
		else v += ((-v) / MOD + 1)*MOD;
		v %= MOD;
	}
	void operator = (const ModInt& right) { v = right.v; }
	template<class T> void operator = (const T& right) {
		v = right;
		if (v >= 0) v %= MOD;
		else v = v += ((-v) / MOD + 1)*MOD;
		v %= MOD;
	}

	ModInt operator + (const ModInt& right) { return (v + right.v) % MOD; }
	ModInt operator - (const ModInt& right) { return (MOD - (v - right.v)); }
	ModInt operator * (const ModInt& right) { return (v * right.v) % MOD; }
	ModInt operator / (const ModInt& right) { return v / right.v; }

	void operator += (const ModInt& right) { v = (v + right.v) % MOD; }
	void operator -= (const ModInt& right) { v = (MOD - (v - right.v)); }
	void operator *= (const ModInt& right) { v = (v* right.v) % MOD; }
	void operator /= (const ModInt& right) { v = v / right.v; }

	bool operator == (const ModInt& right) { return v == right.v; }
};

ostream& operator << (ostream& os, const ModInt& value) {
	os << value.v;
	return os;
}

void solve();
/// ---template---

signed main(void) {
	SETUP;
	solve();
	return 0;
}

vector<vector<int> > G;

list<int> DFS(int v, vector<bool>& visited) {
	visited[v] = true;
	bool isVisit = false;
	list<int> res;
	for (auto &t : G[v]) {
		if (not visited[t]) {
			res.splice(res.end(), DFS(t, visited));
			isVisit = true;
			break;
		}
	}
	res.push_back(v);
	return res;
}

void solve() {
	int N, M; cin >> N >> M;
	vector<pii> edge(N);

	G.resize(N);

	REP(i, M) {
		int A, B;
		cin >> A >> B;
		--A; --B;
		G[A].push_back(B);
		G[B].push_back(A);
	}

	int start = 0;
	vector<bool> visited(N);
	list<int> path1 = DFS(start, visited);
	for (auto &a : path1) visited[a] = true;
	list<int> path2 = DFS(start, visited);
	path2.pop_back();
	cout << path1.size() + path2.size() << endl;
	for (auto &a : path2) {
		cout << a+1 << " ";
	}
	for (auto it = path1.rbegin(); it != path1.rend(); ++it) {
		cout << *it+1 << " ";
	}
	cout << endl;
}


Measured memory_bytes: 16768