#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ii = pair<ll, ll>;
#define foru(i, l, r) for(int i=(l); i<=(r); ++i)
#define ford(i, l, r) for(int i=(l); i>=(r); --i)
#define fore(x, v) for(auto &x : v)
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
#define fi first
#define se second
#define file "input"
template<class T> bool minimize(T &a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<class T> bool maximize(T &a, T b) { if (a < b) { a = b; return 1; } return 0; }
void setIO() {
ios::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
if (fopen(file".inp", "r")) {
freopen(file".inp", "r", stdin);
freopen(file".out", "w", stdout);
}
}
const int N = 5e5+5;
int n, k;
vector<int> adj[N];
bool sheep[N];
void solve1() {
vector<int> rem;
foru(i, 1, n) if (sheep[i]) rem.push_back(i);
sort(all(rem));
vector<int> ans;
while (!rem.empty()) {
int u = rem.back();
if (rem.size() >= 2 && (rem[sz(rem)-2]+u)%2==0) {
int v = rem[sz(rem)-2];
ans.push_back((u+v)/2);
rem.pop_back();
} else ans.push_back(u);
rem.pop_back();
}
cout << sz(ans) << "\n";
fore(x, ans) cout << x << " ";
}
int kth[N], DP[1<<15], F[1<<15];
ii T[1<<15];
void solve2() {
memset(DP, 0x3f, sizeof(DP));
queue<int> qu;
vector<int> tmp;
vector<vector<int>> dist;
int id=0;
foru(i, 1, n) if (sheep[i]) {
tmp.push_back(i);
queue<int> qu;
qu.push(i);
dist.push_back(vector<int>(n+1, -1));
dist[id][i] = 0;
while (!qu.empty()) {
int u = qu.front();
qu.pop();
fore(v, adj[u]) if (dist[id][v] == -1) {
dist[id][v] = dist[id][u]+1;
qu.push(v);
}
}
kth[i] = id++;
}
foru(i, 1, n) {
int mask = 0;
int mn = N;
fore(v, tmp)
if (dist[kth[v]][i] < mn) {
mn = dist[kth[v]][i];
mask = 1<<kth[v];
}
else if (dist[kth[v]][i] == mn)
mask += 1<<kth[v];
F[mask] = i;
}
int full = (1<<id)-1;
DP[0] = 0;
foru(m, 0, full) {
for(int sub=m; sub>0; sub=(sub-1)&m) if (F[sub] > 0) {
if (minimize(DP[m], DP[m^sub] + 1)) {
T[m].fi = sub;
T[m].se = m^sub;
}
}
for(int sub=m; sub>0; sub=(sub-1)&m)
if (minimize(DP[sub], DP[m])) {
T[sub].fi = -1;
T[sub].se = m;
}
}
cout << DP[full] << "\n";
vector<int> shepherd;
while(full > 0) {
if (T[full].fi != -1) shepherd.push_back(F[T[full].fi]);
full = T[full].se;
}
fore(x, shepherd) {
cout << x << " ";
}
}
int vis[N], dist[N], high[N], up[N];
int mark[N*2];
vector<int> block[N];
// dist[v] + high[v] == high[u]
void dfs_first(int u, int p) {
if (!mark[dist[u]+high[u]]) mark[dist[u]+high[u]] = u;
if (sheep[u]) {
assert(mark[high[u]] > 0);
up[u] = mark[high[u]];
block[high[u]].push_back(u);
}
fore(v, adj[u]) {
if (v == p) continue;
high[v] = high[u]+1;
dfs_first(v, u);
}
if (mark[dist[u]+high[u]] == u) mark[dist[u]+high[u]] = 0;
}
void dfs_second(int u) {
vis[u] = 1;
fore(v, adj[u]) {
if (vis[v]) continue;
if (dist[u]==dist[v]+1) dfs_second(v);
}
}
void solve3() {
queue<int> qu;
memset(dist, -1, sizeof(dist));
foru(i, 1, n) if (sheep[i]) { dist[i] = 0; qu.push(i); }
while (!qu.empty()) {
int u = qu.front();
qu.pop();
fore(v, adj[u]) if (dist[v] == -1) { dist[v] = dist[u]+1; qu.push(v); }
}
dfs_first(1, 0);
vector<int> ans;
ford(i, n, 0) if (!block[i].empty()) {
fore(u, block[i]) if (!vis[u]) {
ans.push_back(up[u]);
dfs_second(up[u]);
}
}
cout << sz(ans) << "\n";
fore(x, ans) cout << x << " ";
}
int main() {
setIO();
bool line = 1;
cin >> n >> k;
foru(i, 2, n) {
int u, v;
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
foru(i, 1, k) {
int node;
cin >> node;
sheep[node] = 1;
}
foru(i, 1, n)
line &= (sz(adj[i]) <= 2);
line &= sz(adj[1]) == 1;
line &= sz(adj[n]) == 1;
solve3();
// if (line) solve1();
// else if (k <= 15) solve2();
// else solve3();
}
