#include <iostream>
#include <map>
#include <vector>
#include <fstream>

using namespace std;

int main(){

	ios_base::sync_with_stdio(false);
	cin.tie(NULL);

    ifstream in("maxpath.in");
    cin.rdbuf(in.rdbuf());

    ofstream out("maxpath.out");
    cout.rdbuf(out.rdbuf());

    int N, M;
    map<int, vector<int> > edges;

    cin >> N >> M;

    vector<int> path;

    for(int i = 1; i <= N; i++){
        edges.insert(make_pair(i, path));
    }

    for(int i = 0; i < M; i++){
        int from, to;
        cin >> from >> to;

        map<int, vector<int> >::iterator it = edges.find(from);
        it->second.push_back(to);
        it = edges.find(to);
        it->second.push_back(from);
    }

    map<int, vector<int> >::iterator it = edges.begin();
    path.push_back(it->first);

    bool b = true;

    while(true){
        int index = 0;
        for(auto el : it->second){
            b = true;
           // cout << "ot " << it->first << " vzimam - " << el;
            for(auto e : path){
                if(el == e){
                    b = false;
                }
            }

            if(b){
              //  cout << "svobodno e";
                break;
            }
            //cout << " veche e izbrano" << endl;

            index++;
        }

        if(!b) break;

        it = edges.find(it->second[index]);
        path.push_back(it->first);
    }

    cout << path.size() << endl;

    for(auto el : path) cout << el << endl;

}