#include <stdio.h>
#include <stdlib.h>
#define graph_valtype int

typedef struct graph_edge_sub graph_edge;

typedef struct {
	int num;
	int next_num;
	graph_edge *next;
	int prev_num;
}graph_vertex_sub;

struct graph_edge_sub{
	graph_vertex_sub *v;
	int w;
	graph_edge *next;
};

typedef struct graph_v_sub graph_vertex;

struct graph_v_sub{
	int num;
	graph_valtype val;
	int next_num;
	graph_vertex **next;
	int *next_weight;
	int prev_num;
	graph_vertex **prev;
	int *prev_weight;
};

typedef struct {
	int N;
	graph_vertex_sub **v_s;
	graph_vertex **v;
}graph;

//頂点数N, 各頂点の初期値ini_valのグラフを作る
graph *make_graph(int N, graph_valtype ini_val){
	int i;
	graph *g = (graph *)malloc(sizeof(graph));
	g->N = N;
	g->v_s = (graph_vertex_sub **)malloc(sizeof(graph_vertex_sub *) * N);
	g->v = (graph_vertex **)malloc(sizeof(graph_vertex *) * N);
	for(i = 0; i < N; i++){
		(g->v_s)[i] = (graph_vertex_sub *)malloc(sizeof(graph_vertex_sub));
		(g->v_s)[i]->num = i;
		(g->v_s)[i]->next_num = 0;
		(g->v_s)[i]->next = NULL;
		(g->v_s)[i]->prev_num = 0;
		(g->v)[i] = (graph_vertex *)malloc(sizeof(graph_vertex));
		(g->v)[i]->num = i;
		(g->v)[i]->val = ini_val;
		(g->v)[i]->next_num = 0;
		(g->v)[i]->next = NULL;
		(g->v)[i]->next_weight = NULL;
		(g->v)[i]->prev_num = 0;
		(g->v)[i]->prev = NULL;
		(g->v)[i]->prev_weight = NULL;
	}
	return g;
}

//グラフgの頂点aから頂点bに重みwの有向辺を張る (0 <= a, b <= N - 1)
void set_edge_graph(int a, int b, int w, graph *g){
	graph_edge *new1 = (graph_edge *)malloc(sizeof(graph_edge));
	new1->v = (g->v_s)[b];
	new1->w = w;
	new1->next = (g->v_s)[a]->next;
	(g->v_s)[a]->next = new1;
	(g->v_s)[a]->next_num++;
	(g->v_s)[b]->prev_num++;
}

//set_edge_graph後に呼び出す
void build_graph(graph *g){
	int i;
	graph_vertex_sub **v_s = g->v_s;
	graph_vertex **v = g->v;
	graph_vertex *nowv;
	graph_edge *nowe;
	for(i = 0; i < g->N; i++){
		v[i]->next = (graph_vertex **)malloc(sizeof(graph_vertex *) * v_s[i]->next_num);
		v[i]->next_weight = (int *)malloc(sizeof(int) * v_s[i]->next_num);
		v[i]->prev = (graph_vertex **)malloc(sizeof(graph_vertex *) * v_s[i]->prev_num);
		v[i]->prev_weight = (int *)malloc(sizeof(int) * v_s[i]->prev_num);
	}
	for(i = 0; i < g->N; i++){
		nowv = v[i];
		for(nowe = v_s[i]->next; nowe != NULL; nowe = nowe->next){
			(nowv->next)[nowv->next_num] = v[nowe->v->num];
			(nowv->next_weight)[nowv->next_num] = nowe->w;
			nowv->next_num++;
			(v[nowe->v->num]->prev)[v[nowe->v->num]->prev_num] = nowv;
			(v[nowe->v->num]->prev_weight)[v[nowe->v->num]->prev_num] = nowe->w;
			v[nowe->v->num]->prev_num++;
		}
	}
}

void output1(graph_vertex *nowv){
	int i;
	for(i = 0; i < nowv->next_num; i++){
		if(nowv->next_weight[i] == 1){
			break;
		}
	}
	if(i < nowv->next_num){
		output1(nowv->next[i]);
	}
	printf("%d ", nowv->num + 1);
}

void output2(graph_vertex *nowv){
	printf("%d ", nowv->num + 1);
	int i;
	for(i = 0; i < nowv->next_num; i++){
		if(nowv->next_weight[i] == 1){
			break;
		}
	}
	if(i < nowv->next_num){
		output2(nowv->next[i]);
	}
}

int main(){
	int N, M, A, B, i;
	scanf("%d%d", &N, &M);
	graph *g = make_graph(N, 0);
	for(i = 0; i < M; i++){
		scanf("%d%d", &A, &B);
		A--;
		B--;
		set_edge_graph(A, B, 0, g);
		set_edge_graph(B, A, 0, g);
	}
	build_graph(g);
	graph_vertex *nowv = g->v[0];
	nowv->val = 1;
	int ans = 1;
	for(;;){
		for(i = 0; i < nowv->next_num; i++){
			if(nowv->next_weight[i] == 0 && nowv->next[i]->val == 0){
				break;
			}
		}
		if(i == nowv->next_num){
			break;
		}
		else{
			ans++;
			nowv->next_weight[i] = 1;
			nowv = nowv->next[i];
			nowv->val = 1;
		}
	}
	nowv = g->v[0];
	for(;;){
		for(i = 0; i < nowv->next_num; i++){
			if(nowv->next_weight[i] == 0 && nowv->next[i]->val == 0){
				break;
			}
		}
		if(i == nowv->next_num){
			break;
		}
		else{
			ans++;
			nowv->next_weight[i] = 1;
			nowv = nowv->next[i];
			nowv->val = 1;
		}
	}
	printf("%d\n", ans);
	output1(g->v[0]->next[0]);
	g->v[0]->next_weight[0] = 0;
	output2(g->v[0]);
	return 0;
}

Measured memory_bytes: 30464