/*
* C++11 code template for contests.
* @author: Andrey Kalendarov
* @e-mail: andreykalendarov@gmail.com
*/

//#pragma GCC optimize ("O3")
//#define ANDREIKKAA_TOPCODER
//#define ANDREIKKAA_ALLOCATOR
#define ANDREIKKAA_CLASS Solution
#define ANDREIKKAA_METHOD solve
#define ANDREIKKAA_PARAMETERS void
#define ANDREIKKAA_CALL
#define ANDREIKKAA_RETURN_TYPE void

#define first x
#define second y
#include "bits/stdc++.h"
using namespace std;

typedef long long ll;
typedef long double ld;

#define endl '\n'
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
const ld PI = acos(-1);

const int _ML = 500;
const char _inpf[] =
#if defined(ANDREIKKAA)
"input.txt"
#else
""
#endif
;
const char _outf[] =
#if defined(ANDREIKKAA)
""
#else
""
#endif
;

#if defined(ANDREIKKAA_ALLOCATOR)
char _mem[_ML * 1024LL * 1024LL];
size_t _ptr = 0;
inline void* operator new(size_t _x) { _ptr += _x; return _mem + _ptr - _x; }
inline void operator delete(void*) { }
#endif

template<typename T, typename U> inline ostream &operator << (ostream &_out, const pair<T, U> &_p) { _out << _p.first << ' ' << _p.second; return _out; }
template<typename T, typename U> inline istream &operator >> (istream &_in, pair<T, U> &_p) { _in >> _p.first >> _p.second; return _in; }
template<typename T> inline ostream &operator << (ostream &_out, const vector<T> &_v) { if (_v.empty()) return _out; _out << _v.front(); for (auto _it = ++_v.begin(); _it != _v.end(); ++_it) _out << ' ' << *_it; return _out; }
template<typename T> inline istream &operator >> (istream &_in, vector<T> &_v) { for (auto &_i : _v) _in >> _i; return _in; }
template<typename T> inline ostream &operator << (ostream &_out, const set<T> &_s) { if (_s.empty()) return _out; _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) _out << ' ' << *_it; return _out; }
template<typename T> inline ostream &operator << (ostream &_out, const multiset<T> &_s) { if (_s.empty()) return _out; _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) _out << ' ' << *_it; return _out; }
template<typename T> inline ostream &operator << (ostream &_out, const unordered_set<T> &_s) { if (_s.empty()) return _out; _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) _out << ' ' << *_it; return _out; }
template<typename T> inline ostream &operator << (ostream &_out, const unordered_multiset<T> &_s) { if (_s.empty()) return _out; _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) _out << ' ' << *_it; return _out; }
template<typename T, typename U> inline ostream &operator << (ostream &_out, const map<T, U> &_m) { if (_m.empty()) return _out; _out << '(' << _m.begin()->first << ": " << _m.begin()->second << ')'; for (auto _it = ++_m.begin(); _it != _m.end(); ++_it) _out << ", (" << _it->first << ": " << _it->second << ')'; return _out; }
template<typename T, typename U> inline ostream &operator << (ostream &_out, const unordered_map<T, U> &_m) { if (_m.empty()) return _out; _out << '(' << _m.begin()->first << ": " << _m.begin()->second << ')'; for (auto _it = ++_m.begin(); _it != _m.end(); ++_it) _out << ", (" << _it->first << ": " << _it->second << ')'; return _out; }

/* ________ CODE ________ */

inline ANDREIKKAA_RETURN_TYPE mainFunction(ANDREIKKAA_PARAMETERS)
{
	int n, m;
	cin >> n >> m;

	const int N = 100 * 1000 + 228;
	static vector<int> g[N];
	for (int i = 0; i < m; ++i)
	{
		int a, b;
		cin >> a >> b;
		g[a].push_back(b);
		g[b].push_back(a);
	}

	vector<bool> u(n + 1);
	u[1] = true;
	deque<int> d;
	d.push_back(1);
	vector<int> ptr(n + 1);

	while (true)
	{
	ok:;
		for (; ptr[d.front()] < sz(g[d.front()]); ++ptr[d.front()])
		{
			if (!u[g[d.front()][ptr[d.front()]]])
			{
				u[g[d.front()][ptr[d.front()]]] = true;
				d.push_front(g[d.front()][ptr[d.front()]]);
				goto ok;
			}
		}
		for (; ptr[d.back()] < sz(g[d.back()]); ++ptr[d.back()])
		{
			if (!u[g[d.back()][ptr[d.back()]]])
			{
				u[g[d.back()][ptr[d.back()]]] = true;
				d.push_back(g[d.back()][ptr[d.back()]]);
				goto ok;
			}
		}
		break;
	}

	cout << sz(d) << endl;
	for (int i : d)
		cout << i << " ";
	cout << endl;
}

/* ________ CODE ________ */

#if defined(ANDREIKKAA) || !defined(ANDREIKKAA_TOPCODER)
int main()
{
#if defined(ANDREIKKAA)
	time_t _start = clock();
#endif
	if (_inpf[0] != '\0')
		assert(freopen(_inpf, "r", stdin) != nullptr);
	if (_outf[0] != '\0')
		assert(freopen(_outf, "w", stdout) != nullptr);
	cin.tie(nullptr);
	ios_base::sync_with_stdio(false);
	cout << setprecision(20);
	//cout << fixed;	
	mainFunction(ANDREIKKAA_CALL);
#if defined(ANDREIKKAA)
	cerr << "Time: " << (clock() - _start) / (ld)CLOCKS_PER_SEC << endl;
	while (true);
#endif
}
#else
class ANDREIKKAA_CLASS { public: ANDREIKKAA_RETURN_TYPE ANDREIKKAA_METHOD(ANDREIKKAA_PARAMETERS) { return mainFunction(ANDREIKKAA_CALL); } };
#endif

Measured memory_bytes: 7168