#include <bits/stdc++.h>
using namespace std;

#define forr(x,arr) for(auto&& x:arr)
#define _overload3(_1,_2,_3,name,...) name
#define _rep2(i,n) _rep3(i,0,n)
#define _rep3(i,a,b) for(int i=int(a);i<int(b);++i)
#define rep(...) _overload3(__VA_ARGS__,_rep3,_rep2,)(__VA_ARGS__)
#define _rrep2(i,n) _rrep3(i,0,n)
#define _rrep3(i,a,b) for(int i=int(b)-1;i>=int(a);i--)
#define rrep(...) _overload3(__VA_ARGS__,_rrep3,_rrep2,)(__VA_ARGS__)
#define all(x) (x).begin(),(x).end()
#define bit(n) (1LL<<(n))
#define sz(x) ((int)(x).size())
#define TEN(n) ((ll)(1e##n))
#define fst first
#define snd second

string DBG_DLM(int &i){return(i++==0?"":", ");}
#define DBG_B(exp){int i=0;os<<"{";{exp;}os<<"}";return os;}
template<class T>ostream&operator<<(ostream&os,vector<T>v);
template<class T>ostream&operator<<(ostream&os,set<T>v);
template<class T>ostream&operator<<(ostream&os,queue<T>q);
template<class T>ostream&operator<<(ostream&os,priority_queue<T>q);
template<class T,class K>ostream&operator<<(ostream&os,pair<T,K>p);
template<class T,class K>ostream&operator<<(ostream&os,map<T,K>mp);
template<class T,class K>ostream&operator<<(ostream&os,unordered_map<T,K>mp);
template<int I,class TPL>void DBG(ostream&os,TPL t){}
template<int I,class TPL,class H,class...Ts>void DBG(ostream&os,TPL t){os<<(I==0?"":", ")<<get<I>(t);DBG<I+1,TPL,Ts...>(os,t);}
template<class T,class K>void DBG(ostream&os,pair<T,K>p,string delim){os<<"("<<p.first<<delim<<p.second<<")";}
template<class...Ts>ostream&operator<<(ostream&os,tuple<Ts...>t){os<<"(";DBG<0,tuple<Ts...>,Ts...>(os,t);os<<")";return os;}
template<class T,class K>ostream&operator<<(ostream&os,pair<T,K>p){DBG(os,p,", ");return os;}
template<class T>ostream&operator<<(ostream&os,vector<T>v){DBG_B(forr(t,v){os<<DBG_DLM(i)<<t;});}
template<class T>ostream&operator<<(ostream&os,set<T>s){DBG_B(forr(t,s){os<<DBG_DLM(i)<<t;});}
template<class T>ostream&operator<<(ostream&os,queue<T>q){DBG_B(for(;q.size();q.pop()){os<<DBG_DLM(i)<<q.front();});}
template<class T>ostream&operator<<(ostream&os,priority_queue<T>q){DBG_B(for(;q.size();q.pop()){os<<DBG_DLM(i)<<q.top();});}
template<class T,class K>ostream&operator<<(ostream&os,map<T,K>m){DBG_B(forr(p,m){os<<DBG_DLM(i);DBG(os,p,"->");});}
template<class T,class K>ostream&operator<<(ostream&os,unordered_map<T,K>m){DBG_B(forr(p,m){os<<DBG_DLM(i);DBG(os,p,"->");});}
#define DBG_OVERLOAD(_1,_2,_3,_4,_5,_6,macro_name,...)macro_name
#define DBG_LINE(){char s[99];sprintf(s,"line:%3d | ",__LINE__);cerr<<s;}
#define DBG_OUTPUT(v){cerr<<(#v)<<"="<<(v);}
#define DBG1(v,...){DBG_OUTPUT(v);}
#define DBG2(v,...){DBG_OUTPUT(v);cerr<<", ";DBG1(__VA_ARGS__);}
#define DBG3(v,...){DBG_OUTPUT(v);cerr<<", ";DBG2(__VA_ARGS__);}
#define DBG4(v,...){DBG_OUTPUT(v);cerr<<", ";DBG3(__VA_ARGS__);}
#define DBG5(v,...){DBG_OUTPUT(v);cerr<<", ";DBG4(__VA_ARGS__);}
#define DBG6(v,...){DBG_OUTPUT(v);cerr<<", ";DBG5(__VA_ARGS__);}
#define DEBUG0(){DBG_LINE();cerr<<endl;}
#ifdef LOCAL
#define out(...){DBG_LINE();DBG_OVERLOAD(__VA_ARGS__,DBG6,DBG5,DBG4,DBG3,DBG2,DBG1)(__VA_ARGS__);cerr<<endl;}
#else
#define out(...)
#endif

using ll=long long;
using pii=pair<int,int>;using pll=pair<ll,ll>;using pil=pair<int,ll>;using pli=pair<ll,int>;
using vs=vector<string>;using vvs=vector<vs>;using vvvs=vector<vvs>;
using vb=vector<bool>;using vvb=vector<vb>;using vvvb=vector<vvb>;
using vi=vector<int>;using vvi=vector<vi>;using vvvi=vector<vvi>;
using vl=vector<ll>;using vvl=vector<vl>;using vvvl=vector<vvl>;
using vd=vector<double>;using vvd=vector<vd>;using vvvd=vector<vvd>;
using vpii=vector<pii>;using vvpii=vector<vpii>;using vvvpii=vector<vvpii>;
template<class A,class B>bool amax(A&a,const B&b){return b>a?a=b,1:0;}
template<class A,class B>bool amin(A&a,const B&b){return b<a?a=b,1:0;}
ll ri(){ll l;cin>>l;return l;} string rs(){string s;cin>>s;return s;}

using Weight = int;
struct Edge {
  int dst;
  Weight weight;
  Edge() : dst(0), weight(0) {}
  Edge(int d, Weight w = 1) : dst(d), weight(w) {}
};
using Edges = vector<Edge>;
using Graph = vector<Edges>;


struct UnionFind {
  const int V;
  vector<int> par, rank, cnt;
  UnionFind(int V) : V(V), par(V), rank(V), cnt(V) { init(); }

  void init() {
    for (int i = 0; i < V; i++) par[i] = i;
    fill(rank.begin(), rank.end(), 0);
    fill(cnt.begin(), cnt.end(), 1);
  }

  int find(int x) {
    return par[x] == x ? x : par[x] = find(par[x]);
  }

  bool unite(int x, int y) {
    if ((x = find(x)) == (y = find(y))) return false;
    cnt[y] = cnt[x] = cnt[x] + cnt[y];

    if (rank[x] < rank[y]) par[x] = y;
    else {
      par[y] = x;
      if (rank[x] == rank[y]) rank[x]++;
    }
    return true;
  }

  bool same(int x, int y) {
    return find(x) == find(y);
  }

  int count(int x) {
    return cnt[find(x)];
  }
};

void Main() {
  int n = ri();
  int m = ri();
  Graph G(n);

  rep(i, m) {
    int u = ri() - 1;
    int v = ri() - 1;
    G[u].emplace_back(v);
    G[v].emplace_back(u);
  }

  UnionFind uf(n);

  uf.unite(0, G[0][0].dst);

  vector<int> H, T;
  H.push_back(0);

  while (1) {
    int u = H.back();
    bool ok = 1;
    forr(v, G[u]) {
      if (!uf.same(0, v.dst)) {
        uf.unite(0, v.dst);
        H.emplace_back(v.dst);
        ok = false;
        break;
      }
    }
    if (ok) break;
  }

  T.emplace_back(G[0][0].dst);
  while (1) {
    int u = T.back();
    bool ok = 1;
    forr(v, G[u]) {
      if (!uf.same(0, v.dst)) {
        uf.unite(0, v.dst);
        T.emplace_back(v.dst);
        ok = false;
        break;
      }
    }
    if (ok) break;
  }

  out(H);
  out(T);

  reverse(all(H));
  int sz = sz(H) + sz(T);
  vi ans;
  forr(h, H) ans.emplace_back(h+1);
  forr(t, T) ans.emplace_back(t+1);

  cout << sz << endl;
  rep(i, sz) {
    cout << ans[i];
    if (i + 1 < sz) cout << ' ';
    else cout << endl;
  }

}

signed main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  Main();
  return 0;
}

Measured memory_bytes: 8504