#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define fi first
#define se second
#define vi vector<int>
#define vll vector<long long>
#define pii pair<int, int>
#define pll pair<long long, long long>
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
mt19937_64 rng64(chrono::high_resolution_clock::now().time_since_epoch().count());
inline int rand(int l,int r){return uniform_int_distribution<int>(l, r)(rng);}
inline ll rand(ll l,ll r){return uniform_int_distribution<ll>(l, r)(rng64);}
#ifdef DEBUG
auto&operator<<(auto&o,pair<auto,auto>p){return o<<"("<<p.first<<", "<<p.second<<")";}
auto operator<<(auto&o,auto x)->decltype(x.end(),o){o<<"{";int i=0;for(auto e:x)o<<","+!i++<<e;return o<<"}";}
#define debug(X...)cerr<<"["#X"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(X)
#else
#define debug(...){}
#endif
struct custom_hash {
static uint64_t splitmix64(uint64_t x) {
x += 0x9e3779b97f4a7c15;
x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
return x ^ (x >> 31);
}
size_t operator()(uint64_t x) const {
static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
return splitmix64(x + FIXED_RANDOM);
}
};
struct pair_hash{
size_t operator()(const pair<int,int>&x)const{
return hash<long long>()(((long long)x.first)^(((long long)x.second)<<32));
}
};
const int MAXN = 5e5 + 7;
vi g[MAXN];
int f[MAXN];
int dist[MAXN];
int n, k;
vi ans = {};
pii dfs(int v, int p){
int curr = (dist[v] == 0 ? 0 : -1);
int up = -1;
for(auto u : g[v]){
if(u == p){
continue;
}
pii ret = dfs(u, v);
if(ret.fi != -1){
curr = ret.fi + 1;
}else if(ret.se != -1){
up = max(up, ret.se - 1);
}
}
//cout << v << ' ' << curr << ' ' << up << '\n';
if(up >= curr || curr == -1){
return mp(-1, up);
}
if(p != v && dist[p] == curr + 1){
return mp(curr, -1);
}else{
// cout << "BUILD: " << v << '\n';
ans.pb(v);
return mp(-1, curr);
}
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(NULL);
cout.tie(NULL);
cin >> n >> k;
for(int i = 1; i < n; i++){
int a, b;
cin >> a >> b;
g[a].pb(b);
g[b].pb(a);
}
queue<int> q;
for(int i = 1; i <= k; i++){
int x;
cin >> x;
f[x] = 1;
dist[x] = 0;
q.push(x);
}
while(sz(q)){
int v = q.front();
q.pop();
for(auto u : g[v]){
if(f[u]){
continue;
}
f[u] = 1;
dist[u] = dist[v] + 1;
q.push(u);
}
}
dfs(1, 1);
cout << sz(ans) << '\n';
for(auto ele : ans){
cout << ele << ' ';
}
cout << '\n';
return 0;
}
