import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.Closeable;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;
import java.util.HashMap;
import java.util.List;

public class Main {
	static ContestScanner in;
	static Writer out;
	public static void main(String[] args) {
		Main main = new Main();
		try {
			in = new ContestScanner();
			out = new Writer();
			main.solve();
			out.close();
			in.close();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	
	void solve() throws IOException {
		int n = in.nextInt();
		int m = in.nextInt();
		List<Integer>[] node = new List[n];
		for(int i = 0; i < n; i++) node[i] = new ArrayList<>();
		for(int i = 0; i < m; i++) {
			int a = in.nextInt() - 1;
			int b = in.nextInt() - 1;
			node[a].add(b);
			node[b].add(a);
		}
		boolean[] used = new boolean[n];
		Deque<Integer> qu = new ArrayDeque<>();
		boolean hasNext = true;
		int top = 0;
		qu.addFirst(top);
		used[top] = true;
		while(hasNext) {
			hasNext = false;
			for(int nv: node[top]) {
				if(used[nv]) continue;
				used[nv] = true;
				hasNext = true;
				top = nv;
				qu.addFirst(top);
				break;
			}
		}
		top = 0;
		hasNext = true;
		while(hasNext) {
			hasNext = false;
			for(int nv: node[top]) {
				if(used[nv]) continue;
				used[nv] = true;
				hasNext = true;
				top = nv;
				qu.addLast(top);
				break;
			}
		}
		out.println(qu.size());
		while(!qu.isEmpty()) {
			int v = qu.poll();
			out.print(v + 1);
			if(!qu.isEmpty()) out.print(" ");
		}
		out.println();
	}
}

@SuppressWarnings("serial")
class MultiSet<T> extends HashMap<T, Integer>{
	@Override public Integer get(Object key){return containsKey(key)?super.get(key):0;}
	public void add(T key,int v){put(key,get(key)+v);}
	public void add(T key){put(key,get(key)+1);}
	public void sub(T key){final int v=get(key);if(v==1)remove(key);else put(key,v-1);}
	public MultiSet<T> merge(MultiSet<T> set)
	{MultiSet<T>s,l;if(this.size()<set.size()){s=this;l=set;}else{s=set;l=this;}
	for(Entry<T,Integer>e:s.entrySet())l.add(e.getKey(),e.getValue());return l;}
}

class Writer extends PrintWriter{
	public Writer(String filename)throws IOException
	{super(new BufferedWriter(new FileWriter(filename)));}
	public Writer()throws IOException{super(System.out);}
}
class ContestScanner implements Closeable{
	private BufferedReader in;private int c=-2;
	public ContestScanner()throws IOException 
	{in=new BufferedReader(new InputStreamReader(System.in));}
	public ContestScanner(String filename)throws IOException
	{in=new BufferedReader(new InputStreamReader(new FileInputStream(filename)));}
	public String nextToken()throws IOException {
		StringBuilder sb=new StringBuilder();
		while((c=in.read())!=-1&&Character.isWhitespace(c));
		while(c!=-1&&!Character.isWhitespace(c)){sb.append((char)c);c=in.read();}
		return sb.toString();
	}
	public String readLine()throws IOException{
		StringBuilder sb=new StringBuilder();if(c==-2)c=in.read();
		while(c!=-1&&c!='\n'&&c!='\r'){sb.append((char)c);c=in.read();}
		return sb.toString();
	}
	public long nextLong()throws IOException,NumberFormatException
	{return Long.parseLong(nextToken());}
	public int nextInt()throws NumberFormatException,IOException
	{return(int)nextLong();}
	public double nextDouble()throws NumberFormatException,IOException 
	{return Double.parseDouble(nextToken());}
	public void close() throws IOException {in.close();}
}

Measured memory_bytes: 57124