// Author: Teoman Ata Korkmaz
#pragma GCC optimize("O3,unroll-loops,no-stack-protector")
#include <bits/stdc++.h>
#define int int_fast64_t
using namespace std;
constexpr int N=2e5+5;
///////////////////////////////////////////////////////////
int n,m,last[N],depth[N],parent[N],sz[N],heavy[N],head[N],id[N],di[N],cnt,vis[2*N],which[2*N];
vector<int> v,adj[N],n_adj[2*N],r_n_adj[2*N],crazy[N],bt;
vector<pair<int,int>> query;
vector<vector<int>> scc;
void dfs(int node=0,int p=0,int d=0){
parent[node]=p;
depth[node]=d;
sz[node]=1;
//cerr<<"dfs:"<<node<<","<<p<<endl;
if(last[v[node]]!=-1)query.push_back({last[v[node]],node});
last[v[node]]=node;
for(const int& i:adj[node]){
if(i==p)continue;
dfs(i,node,d+1);
sz[node]+=sz[i];
if(!heavy[node] || sz[heavy[node]]<sz[i])heavy[node]=i;
}
}
void dfs2(int node=0,int h=0){
id[node]=cnt;
di[cnt++]=node;
head[node]=h;
if(heavy[node])dfs2(heavy[node],h);
else{
int _n=(id[node]-id[head[node]]+1);
crazy[h].resize(2*_n);
for(int i=1;i<_n;i++)crazy[h][i]=n+id[head[node]]+i-1;
for(int i=_n;i<2*_n;i++)crazy[h][i]=v[di[i-_n+id[head[node]]]];
for(int i=1;i<_n;i++){
n_adj[crazy[h][i]].push_back(crazy[h][i<<1]);
n_adj[crazy[h][i]].push_back(crazy[h][(i<<1)|1]);
}
}
for(const int& i:adj[node]){
if(i==parent[node] || i==heavy[node])continue;
dfs2(i,i);
}
}
void debug(){
cerr<<"parent:";for(int i=0;i<n;i++)cerr<<parent[i]+1<<",";cerr<<endl;
cerr<<"depth:";for(int i=0;i<n;i++)cerr<<depth[i]<<",";cerr<<endl;
cerr<<"sz:";for(int i=0;i<n;i++)cerr<<sz[i]<<",";cerr<<endl;
cerr<<"heavy:";for(int i=0;i<n;i++)cerr<<heavy[i]+1<<",";cerr<<endl;
cerr<<"head:";for(int i=0;i<n;i++)cerr<<head[i]+1<<",";cerr<<endl;
cerr<<"id:";for(int i=0;i<n;i++)cerr<<id[i]+1<<",";cerr<<endl;
cerr<<endl;
for(int i=0;i<n;i++){
cerr<<"crazy:";for(const int& j:crazy[i])cerr<<j+1<<",";cerr<<endl;
}
cerr<<"query:";for(auto [a,b]:query)cerr<<"["<<a+1<<","<<b+1<<"] ";cerr<<endl;
cerr<<"----------------------------------------"<<endl;
}
void st_query(int l,int r,int h,int val){
//cerr<<"stquery:"<<l+1<<","<<r+1<<","<<h+1<<","<<val+1<<endl;
int n=crazy[h].size()/2;
for(l+=n,r+=n;l<r;l>>=1,r>>=1){
if(l&1)n_adj[val].push_back(crazy[h][l++]);
if(r&1)n_adj[val].push_back(crazy[h][--r]);
}
}
void hld_query(int a,int b,int val){
//cerr<<"hld:"<<a+1<<","<<b+1<<","<<val+1<<endl;
while(head[a]!=head[b]){
if(depth[a]<depth[b])swap(a,b);
//cerr<<"a,b:"<<a+1<<","<<b+1<<endl;
st_query(0,id[a]-id[head[a]]+1,head[a],val);
a=parent[head[a]];
}
if(depth[a]<depth[b])swap(a,b);
assert(head[a]==head[b]);
st_query(id[b]-id[head[a]],id[a]-id[head[a]]+1,head[a],val);
}
void dfs3(int node){
//cerr<<"dfs3:"<<node<<endl;
if(vis[node]++)return;
for(const int& i:n_adj[node]){
dfs3(i);
}
bt.push_back(node);
}
void dfs4(int node){
//cerr<<"dfs4:"<<node<<endl;
if(vis[node]++)return;
scc.back().push_back(node);
which[node]=scc.size()-1;
for(const int& i:r_n_adj[node]){
dfs4(i);
}
}
void debug2(){
for(int i=0;i<2*n;i++){
cerr<<"n_adj["<<i+1<<"]:";for(const int& j:n_adj[i])cerr<<j+1<<",";cerr<<endl;
}
for(int i=0;i<2*n;i++){
cerr<<"r_n_adj["<<i+1<<"]:";for(const int& j:r_n_adj[i])cerr<<j+1<<",";cerr<<endl;
}
cerr<<"bt:";for(int i=0;i<2*n;i++)cerr<<bt[i]+1<<",";cerr<<endl;
for(int i=0;i<scc.size();i++){
cerr<<"scc["<<i+1<<"]:";for(const int& j:scc[i])cerr<<j+1<<",";cerr<<endl;
}
cerr<<"which:";for(int i=0;i<2*n;i++)cerr<<which[i]+1<<",";cerr<<endl;
}
signed main(void){
memset(last,-1,sizeof(last));
cin>>n>>m;
for(int i=1;i<n;i++){
int x,y;
cin>>x>>y;x--;y--;
adj[x].push_back(y);
adj[y].push_back(x);
}
v.resize(n);
for(auto& i:v){cin>>i;i--;}
dfs();
dfs2();
//debug();
for(int i=0;i<query.size();i++){
auto [x,y]=query[i];
assert(v[x]==v[y]);
//cerr<<"query:"<<x+1<<","<<y+1<<endl;
hld_query(x,y,v[x]);
}
for(int i=0;i<2*n;i++){
n_adj[i].shrink_to_fit();
for(const int& j:n_adj[i])r_n_adj[j].push_back(i);
}
for(int i=0;i<2*n;i++){
dfs3(i);
}
reverse(bt.begin(),bt.end());
memset(vis,0,sizeof(vis));
for(const int& node:bt){
if(vis[node])continue;
scc.push_back({});
dfs4(node);
}
//debug2();
for(int i=0;i<scc.size();i++){
for(const int& j:n_adj[i]){
if(which[i]!=which[j])scc[which[i]].clear();
}
}
/*for(int i=0;i<scc.size();i++){
cerr<<"scc["<<i+1<<"]:";for(const int& j:scc[i])cerr<<j+1<<",";cerr<<endl;
}*/
int ans=12341234;
for(int i=0;i<scc.size();i++){
if(scc[i].empty())continue;
int cnt=-1;
for(const int& j:scc[i])cnt+=(j<m);
if(cnt!=-1)ans=min(ans,cnt);
}
cout<<ans<<endl;
}
