//
//
//  Codeforces: ganariya
//  AtCoder: ganariya2525
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//  MMMMMMMMMMMMMMMMNOtXtdMMMMMNxzZMMNmgHyVVVVVW%..?/(.,(x-..........(HfffpffpffpffWHHffpffppfVyyWMMMMMM


//include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <unordered_map>
#include <climits>
#include <set>
#include <unordered_set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <queue>
#include <random>
#include <complex>
#include <regex>
#include <locale>
#include <random>
#include <type_traits>

using namespace std;

#define SHOW_VECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOW_MAP(v){std::cerr << #v << endl; for(const auto& xxx: v){std::cerr << xxx.first << " " << xxx.second << "\n";}}

using LL = long long;

//~~~~~~~~~~~~~~~~~~~~~_(＾～＾ ｣ ∠)_~~~~~~~~~~~~~~~~~~~~~

constexpr int MAX_V = 100010;
vector<int> G[MAX_V];

int main() {

    int N, M;
    cin >> N >> M;

    vector<int> A(M), B(M);
    for (int i = 0; i < M; i++) {
        cin >> A[i] >> B[i];
        A[i]--, B[i]--;
        G[A[i]].push_back(B[i]);
        G[B[i]].push_back(A[i]);
    }

    deque<int> Q;
    Q.push_front(A[0]);
    Q.push_back(B[0]);

    vector<bool> used(N);
    used[A[0]] = true;
    used[B[0]] = true;

    while (true) {
        bool update = false;
        int u = Q.front();
        for (int i = 0; i < G[u].size(); i++) {
            int to = G[u][i];
            if (used[to])continue;
            used[to] = true;
            update = true;
            Q.push_front(to);
            break;
        }
        int v = Q.back();
        for (int i = 0; i < G[v].size(); i++) {
            int to = G[v][i];
            if (used[to])continue;
            used[to] = true;
            update = true;
            Q.push_back(to);
            break;
        }
        if (!update) break;
    }

    cout << Q.size() << endl;
    for(int i = 0;i<Q.size();i++) cout << Q[i]  + 1 << " ";

}






































Measured memory_bytes: 7552