#include <bits/stdc++.h>
using namespace std;
int a,b;
vector <int> z[500005];
vector <int> v;
int high[500005];
int par[500005][20];
int low[1000005];
bool check[500001];
bool cmp(int a,int b){
return high[a]>high[b];
}
int up[500005];
void dfs(int i,int parent){
for (auto p:z[i]){
if (p==parent){
continue;
}
high[p]=high[i]+1;
par[p][0]=i;
dfs(p,i);
low[i]=min(low[i],low[p]+1);
}
if (check[i]){
low[i]=0;
}
}
void dfs1(int i,int parent ,int pre){
int min1=pre,min2=pre,trace=0;
if (check[i]){
min1=min2=0;
up[i]=0;
}
for (auto p:z[i]){
if (p==parent){
continue;
}
if (min1>low[p]+1){
min1=low[p]+1;
trace=p;
}
}
for (auto p:z[i]){
if (p==parent || p==trace){
continue;
}
if (min2>low[p]+1){
min2=low[p]+1;
}
up[p]=min1+1;
dfs1(p,i,up[p]);
}
if (trace){
up[trace]=min2+1;
dfs1(trace,i,up[trace]);
}
}
bool vis[500005];
int cnt[500005];
void bfs1(){
queue<int> q;
for (auto p:v){
q.push(p);
vis[p]=true;
cnt[p]=0;
}
while (q.size()){
int pos=q.front();
q.pop();
for (auto p:z[pos]){
if (vis[p]){
continue;
}
vis[p]=true;
cnt[p]=cnt[pos]+1;
q.push(p);
}
}
}
vector <int> res;
int jump(int x){
int org=x;
for (int i=19;i>=0;i--){
int nxt=par[x][i];
if (cnt[nxt]==high[org]-high[nxt]){
x=par[x][i];
}
}
return x;
}
void bfs(int sta,int len){
queue<pair<int,int>> q;
q.push({sta,len});
vis[sta]=true;
while (q.size()){
auto [pos,remain]=q.front();
q.pop();
if (remain==0){
continue;
}
for (auto p:z[pos]){
if (vis[p] || (low[p]!=remain-1 && up[p]!=remain-1)){
continue;
}
vis[p]=true;
q.push({p,remain-1});
}
}
}
signed main()
{
// freopen("test.txt", "r", stdin);
// freopen("o2.out", "w", stdout);
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> a >> b;
for (int i=1;i<a;i++){
int x,y;
cin >> x >> y;
z[x].push_back(y);
z[y].push_back(x);
}
for (int i=1;i<=a;i++){
low[i]=1e9;
up[i]=1e9;
}
for (int i=1;i<=b;i++){
int x;
cin >> x;
check[x]=true;
v.push_back(x);
}
high[0]=-1;
par[1][0]=1;
dfs(1,1);
dfs1(1,1,1e9);
// cout << up[4] << "\n";
for (int j=1;j<=19;j++){
for (int i=1;i<=a;i++){
par[i][j]=par[par[i][j-1]][j-1];
}
}
sort(v.begin(),v.end(),cmp);
bfs1();
memset(vis,false,sizeof vis);
// cout << cnt[1] << "\n";
for (auto p:v){
if (vis[p]){
continue;
}
int nxt=jump(p);
//int nxt=p;
// cout << p << " " << nxt << " " << high[p] << "\n";
int len=high[p]-high[nxt];
res.push_back(nxt);
bfs(nxt,len);
}
cout << res.size() << "\n";
for (auto p:res){
cout << p << " ";
}
return 0;
}
/*
7 3 6
2 < 1
5 < 1
7 > 3
1 = 3
4 > 2
5 = 2
bab?a?c
*/
/*
5
10 9 3 6 1
3
2 1 2 4
1 2 4
1 2 2
*/
/*
8
01010101
10111000
*/
/*
freopen("test.txt", "r", stdin);
freopen("o2.out", "w", stdout);
*/
