import java.io.*;
import java.math.BigInteger;
import java.util.*;
import java.util.concurrent.ConcurrentSkipListSet;

public class Main {
    public static void main(String[] args) throws FileNotFoundException {
        ConsoleIO io = new ConsoleIO(new InputStreamReader(System.in), new PrintWriter(System.out));
        //String test = "B-large-practice";
        //ConsoleIO io = new ConsoleIO(new FileReader("D:\\Dropbox\\code\\practice\\jb\\src\\" + test + ".in"), new PrintWriter(new File("D:\\Dropbox\\code\\practice\\jb\\src\\" + test + "-out.txt")));
        //ConsoleIO io = new ConsoleIO(new FileReader("D:\\Dropbox\\Competitions\\GCJ17\\quals\\" + test + ".in"), new PrintWriter(new File("D:\\Dropbox\\Competitions\\GCJ17\\quals\\" + test + "-out.txt")));

        new Main(io).solve();
        io.close();
    }

    ConsoleIO io;
    Main(ConsoleIO io) {
        this.io = io;
    }

    long MOD = 1_000_000_007;
    List<List<Edge>> gr = new ArrayList<>();

    public void solve() {
        int n = io.ri();
        int m = io.ri();
        for(int i= 0;i<n;i++){
            gr.add(new ArrayList<>());
        }
        for(int i = 0;i<m;i++){
            int u = io.ri()-1;
            int v = io.ri()-1;
            Edge e = new Edge(u,v, i);
            gr.get(u).add(e);
            gr.get(v).add(e);
        }
        ev = new boolean[m];
        nv = new boolean[n];
        res = new ArrayList<>();
        int start = 0;
        boolean two = true;
        for(int i = 0;i<n;i++){
            if(gr.get(i).size()==1){
                start = i;
                two = false;
                break;
            }
        }
        if(two) {
            go(start);
            List<Integer> r2 = new ArrayList<>();
            for(int i = res.size()-1;i>=0;i--)
                r2.add(res.get(i));
            res = r2;
            res.add(start);
            go(start);
        }else {
            res.add(start);
            go(start);
        }
        io.writeLine(res.size()+"");

        StringBuilder sb = new StringBuilder();
        for(int i = 0;i<res.size();i++){
            if(i>0)sb.append(' ');
            sb.append(res.get(i)+1);
        }

        io.writeLine(sb.toString());
    }

    boolean[] ev;
    boolean[] nv;
    List<Integer> res;

    public void go(int cur){
        nv[cur] = true;
        List<Edge> ch = gr.get(cur);
        for(int i= 0;i<ch.size();i++){
            Edge e = ch.get(i);
            if(ev[e.id])continue;
            ev[e.id] = true;
            int next = e.a == cur?e.b:e.a;
            if(nv[next])continue;
            res.add(next);
            go(next);
            break;
        }
    }

    class Edge{
        public Edge(int a, int b, int id){
            this.a = a;
            this.b = b;
            this.id = id;
        }
        public int a;
        public int b;
        public int id;
    }

}

class ConsoleIO {
    BufferedReader br;
    PrintWriter out;
    public ConsoleIO(Reader reader, PrintWriter writer){br = new BufferedReader(reader);out = writer;}
    public void flush(){this.out.flush();}
    public void close(){this.out.close();}
    public void writeLine(String s) {this.out.println(s);}
    public void writeInt(int a) {this.out.print(a);this.out.print(' ');}
    public void writeWord(String s){
        this.out.print(s);
    }
    public void writeIntArray(int[] a, int k, String separator) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < k; i++) {
            if (i > 0) sb.append(separator);
            sb.append(a[i]);
        }
        this.writeLine(sb.toString());
    }
    public int read(char[] buf, int len){try {return br.read(buf,0,len);}catch (Exception ex){ return -1; }}
    public String readLine() {try {return br.readLine();}catch (Exception ex){ return "";}}
    public long[] readLongArray() {
        String[]n=this.readLine().trim().split("\\s+");long[]r=new long[n.length];
        for(int i=0;i<n.length;i++)r[i]=Long.parseLong(n[i]);
        return r;
    }
    public int[] readIntArray() {
        String[]n=this.readLine().trim().split("\\s+");int[]r=new int[n.length];
        for(int i=0;i<n.length;i++)r[i]=Integer.parseInt(n[i]);
        return r;
    }
    public int[] readIntArray(int n) {
        int[] res = new int[n];
        char[] all = this.readLine().toCharArray();
        int cur = 0;boolean have = false;
        int k = 0;
        boolean neg = false;
        for(int i = 0;i<all.length;i++){
            if(all[i]>='0' && all[i]<='9'){
                cur = cur*10+all[i]-'0';
                have = true;
            }else if(all[i]=='-') {
                neg = true;
            }
            else if(have){
                res[k++] = neg?-cur:cur;
                cur = 0;
                have = false;
                neg = false;
            }
        }
        if(have)res[k++] = neg?-cur:cur;
        return res;
    }
    public int ri() {
        try {
            int r = 0;
            boolean start = false;
            boolean neg = false;
            while (true) {
                int c = br.read();
                if (c >= '0' && c <= '9') {
                    r = r * 10 + c - '0';
                    start = true;
                } else if (!start && c == '-') {
                    start = true;
                    neg = true;
                } else if (start || c == -1) return neg ? -r : r;
            }
        } catch (Exception ex) {
            return -1;
        }
    }
    public long readLong() {
        try {
            long r = 0;
            boolean start = false;
            boolean neg = false;
            while (true) {
                int c = br.read();
                if (c >= '0' && c <= '9') {
                    r = r * 10 + c - '0';
                    start = true;
                } else if (!start && c == '-') {
                    start = true;
                    neg = true;
                } else if (start || c == -1) return neg ? -r : r;
            }
        } catch (Exception ex) {
            return -1;
        }
    }
    public String readWord() {
        try {
            boolean start = false;
            StringBuilder sb = new StringBuilder();
            while (true) {
                int c = br.read();
                if (c!= ' ' && c!= '\r' && c!='\n' && c!='\t') {
                    sb.append((char)c);
                    start = true;
                } else if (start || c == -1) return sb.toString();
            }
        } catch (Exception ex) {
            return "";
        }
    }
    public char readSymbol() {
        try {
            while (true) {
                int c = br.read();
                if (c != ' ' && c != '\r' && c != '\n' && c != '\t') {
                    return (char) c;
                }
            }
        } catch (Exception ex) {
            return 0;
        }
    }
    //public char readChar(){try {return (char)br.read();}catch (Exception ex){ return 0; }}
}

Measured memory_bytes: 73032