package main

import (
	"bufio"
	"container/list"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	sc := NewScanner()
	N, M := sc.NextInt(), sc.NextInt()
	edge := make([][]int, N+1)
	for i := 1; i <= N; i++ {
		edge[i] = make([]int, 0)
	}
	for i := 0; i < M; i++ {
		A, B := sc.NextInt(), sc.NextInt()
		edge[A] = append(edge[A], B)
		edge[B] = append(edge[B], A)
	}

	mp := map[int]bool{}
	path := list.New()
	path.PushBack(1)
	nx := edge[path.Front().Value.(int)][0]
	mp[1] = true
	path.PushBack(nx)
	mp[nx] = true

	for {

		flag := true
		for _, k := range edge[path.Back().Value.(int)] {
			if _, ok := mp[k]; !ok {
				flag = false
				nx = k
				break
			}
		}
		if !flag {
			mp[nx] = true
			path.PushBack(nx)
			continue
		}

		for _, k := range edge[path.Front().Value.(int)] {
			if _, ok := mp[k]; !ok {
				flag = false
				nx = k
				break
			}
		}
		if flag {
			break
		}

		mp[nx] = true
		path.PushFront(nx)

	}

	fmt.Println(path.Len())
	count := 0
	for e := path.Front(); e != nil; e = e.Next() {
		if count > 0 {
			fmt.Println(" ")
		}
		fmt.Print(e.Value.(int))
		count++
	}
	fmt.Println()

}
func mapToString(arr []int) []string {
	ret := make([]string, len(arr))
	for i := 0; i < len(arr); i++ {
		ret[i] = strconv.Itoa(arr[i])
	}
	return ret
}

func PrintI(args ...int) {
	fmt.Println(strings.Join(mapToString(args), " "))
}

type Scanner struct {
	r   *bufio.Reader
	buf []byte
	p   int
}

func NewScanner() *Scanner {
	rdr := bufio.NewReaderSize(os.Stdin, 1000)
	return &Scanner{r: rdr}
}
func (s *Scanner) Next() string {
	s.pre()
	start := s.p
	for ; s.p < len(s.buf); s.p++ {
		if s.buf[s.p] == ' ' {
			break
		}
	}
	result := string(s.buf[start:s.p])
	s.p++
	return result
}
func (s *Scanner) NextLine() string {
	s.pre()
	start := s.p
	s.p = len(s.buf)
	return string(s.buf[start:])
}
func (s *Scanner) NextInt() int {
	v, _ := strconv.Atoi(s.Next())
	return v
}
func (s *Scanner) NextInt64() int64 {
	v, _ := strconv.ParseInt(s.Next(), 10, 64)
	return v
}

func (s *Scanner) NextIntArray() []int {
	s.pre()
	start := s.p
	result := []int{}
	for ; s.p < len(s.buf)+1; s.p++ {
		if s.p == len(s.buf) || s.buf[s.p] == ' ' {
			v, _ := strconv.ParseInt(string(s.buf[start:s.p]), 10, 0)
			result = append(result, int(v))
			start = s.p + 1
		}
	}

	return result
}
func (s *Scanner) NextInt64Array() []int64 {
	s.pre()
	start := s.p
	result := []int64{}
	for ; s.p < len(s.buf)+1; s.p++ {
		if s.p == len(s.buf) || s.buf[s.p] == ' ' {
			v, _ := strconv.ParseInt(string(s.buf[start:s.p]), 10, 64)
			result = append(result, v)
			start = s.p + 1
		}
	}
	return result
}

func (s *Scanner) NextMap() map[int]bool {
	s.pre()
	start := s.p
	mp := map[int]bool{}
	for ; s.p < len(s.buf); s.p++ {
		if s.buf[s.p] == ' ' {
			v, _ := strconv.Atoi(string(s.buf[start:s.p]))
			mp[v] = true
			start = s.p + 1
		}
	}
	v, _ := strconv.Atoi(string(s.buf[start:s.p]))
	mp[v] = true

	return mp
}

func (s *Scanner) pre() {
	if s.p >= len(s.buf) {
		s.readLine()
		s.p = 0
	}
}
func (s *Scanner) readLine() {
	s.buf = make([]byte, 0)
	for {
		l, p, e := s.r.ReadLine()
		if e != nil {
			panic(e)
		}
		s.buf = append(s.buf, l...)
		if !p {
			break
		}
	}
}


Measured memory_bytes: 15616