import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.NoSuchElementException;


public class Main {
  private static int[][] g;
  public static void main(String[] args) {
    FastScanner sc = new FastScanner();
    int N = sc.nextInt();
    int M = sc.nextInt();
    
    int[] from = new int[M];
    int[] to = new int[M];
    for (int i = 0; i < M; i ++) {
      from[i] = sc.nextInt() - 1;
      to[i] = sc.nextInt() - 1;
    }
    
    g = packU(N, from, to);
    visited = new boolean[N];
    visited[0] = true;

    dfs(0, 0);
    List<Integer> ret = new ArrayList<>();
    for (int v : stack) {
      if (v < 0) {
        break;
      }
      ret.add(v);
    }
    Collections.reverse(ret);

    dfs(0, 0);
    for (int i = 1; ; i ++) {
      if (stack[i] < 0) {
        break;
      }
      ret.add(stack[i]);
    }
    
    StringBuilder sb = new StringBuilder();
    for (int v:  ret) {
      sb.append(v + 1);
      sb.append(" ");
    }
    
    System.out.println(ret.size());
    System.out.println(sb.substring(0, sb.length() - 1));
    
  }
  
  private static boolean[] visited;
  private static int[] stack = new int[1000001];

  private static boolean dfs(int now, int depth) {
    stack[depth] = now;
    boolean flg = true;

    for (int next : g[now]) {
      if (!visited[next]) {
        visited[next] = true;
        boolean ret = dfs(next, depth + 1);
        if (ret) {
          return true;
        }
        visited[next] = false;
        flg = false;
      }
    }

    if (flg) {
      stack[depth + 1] = -1;
    }
    return flg;
  }

  private static int[][] packU(int n, int[] from, int[] to) {
    int[][] g = new int[n][];
    int[] p = new int[n];
    for (int f : from)
        p[f]++;
    for (int t : to)
        p[t]++;
    for (int i = 0; i < n; i++)
        g[i] = new int[p[i]];
    for (int i = 0; i < from.length; i++) {
        g[from[i]][--p[from[i]]] = to[i];
        g[to[i]][--p[to[i]]] = from[i];
    }
    return g;
}
}


class FastScanner {
	public static String debug = null;

	private final InputStream in = System.in;
	private int ptr = 0;
	private int buflen = 0;
	private byte[] buffer = new byte[1024];
	private boolean eos = false;

	private boolean hasNextByte() {
		if (ptr < buflen) {
			return true;
		} else {
			ptr = 0;
			try {
				if (debug != null) {
					buflen = debug.length();
					buffer = debug.getBytes();
					debug = "";
					eos = true;
				} else {
					buflen = in.read(buffer);
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen < 0) {
				eos = true;
				return false;
			} else if (buflen == 0) {
				return false;
			}
		}
		return true;
	}

	private int readByte() {
		if (hasNextByte())
			return buffer[ptr++];
		else
			return -1;
	}

	private static boolean isPrintableChar(int c) {
		return 33 <= c && c <= 126;
	}

	private void skipUnprintable() {
		while (hasNextByte() && !isPrintableChar(buffer[ptr]))
			ptr++;
	}

	public boolean isEOS() {
		return this.eos;
	}

	public boolean hasNext() {
		skipUnprintable();
		return hasNextByte();
	}

	public String next() {
		if (!hasNext())
			throw new NoSuchElementException();
		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while (isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}

	public long nextLong() {
		if (!hasNext())
			throw new NoSuchElementException();
		long n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		}
		while (true) {
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			} else if (b == -1 || !isPrintableChar(b)) {
				return minus ? -n : n;
			} else {
				throw new NumberFormatException();
			}
			b = readByte();
		}
	}

	public int nextInt() {
		return (int) nextLong();
	}

	public long[] nextLongList(int n) {
		return nextLongTable(1, n)[0];
	}

	public int[] nextIntList(int n) {
		return nextIntTable(1, n)[0];
	}

	public long[][] nextLongTable(int n, int m) {
		long[][] ret = new long[n][m];
		for (int i = 0; i < n; i ++) {
			for (int j = 0; j < m; j ++) {
				ret[i][j] = nextLong();
			}
		}
		return ret;
	}

	public int[][] nextIntTable(int n, int m) {
		int[][] ret = new int[n][m];
		for (int i = 0; i < n; i ++) {
			for (int j = 0; j < m; j ++) {
				ret[i][j] = nextInt();
			}
		}
		return ret;
	}
}

Measured memory_bytes: 45864