#include <bits/stdc++.h>
using namespace std;
//#pragma GCC optimize("O3,unroll-loops") //main
//#pragma GCC target("avx2") //cf...
//#pragma GCC target("sse4") //Quera
#define ll long long
typedef pair<int,int> pii;
typedef pair<int,pii> pip;
typedef pair<pii,int> ppi;
typedef pair<pii,pii> ppp;
#define f first
#define s second
#define lc 2*id
#define rc 2*id+1
#define all(x) x.begin(),x.end()
#define pb push_back
#define pp pop_back
#define unicorn(x) x.resize(unique(x.begin(),x.end())-x.begin())
string pr(int* vv,int l,int r){for(int i=l;i<r;i++)cout<<vv[i]<<" ";return "";}
string pr( ll* vv,int l,int r){for(int i=l;i<r;i++)cout<<vv[i]<<" ";return "";}
string pr(vector<int> vv){for(auto i:vv)cout<<i<<" ";return "";}
string pr( vector<ll> vv){for(auto i:vv)cout<<i<<" ";return "";}
string pr(pii* vv,int l,int r){for(int i=l;i<r;i++)cout<<"( "<<vv[i].f<<","<<vv[i].s<<" ) ";return "";}
string pr(vector<pii> vv){for(auto i:vv)cout<<"( "<<i.f<<","<<i.s<<" ) ";return "";}
random_device device;
default_random_engine rng(device());
#define randt(a,b) uniform_int_distribution<int64_t>(a,b)(rng)
const int L = 2e5+10,mod = 1e9+7;
const int inf = 1e9+10;
int n,k,C;
int ans;
int a[L];
vector<int> occ[L],adj[L];
int cnt[L],subt[L];
bool mark[L],isc[L],isv[L];
vector<int> V;
int par[L];
void Find(int v,int p,int sz){
bool ok = 1;
subt[v] = 1;
for(auto u:adj[v]){
if(!mark[u] and u != p){
Find(u,v,sz);
subt[v] += subt[u];
ok = ok and (subt[u]*2 <= sz);
}
}
ok = ok and (subt[v]*2 >= sz);
if(ok)
C = v;
}
void reset(int v,int p){
cnt[a[v]] = isc[a[v]] = 0;
isv[v] = 0;
for(auto u:adj[v]){
if(!mark[u] and u != p){
reset(u,v);
}
}
}
void dfs(int v){
cnt[a[v]]++;
subt[v] = 1;
for(auto u:adj[v]){
if(!mark[u] and u != par[v]){
par[u] = v;
dfs(u);
subt[v] += subt[u];
}
}
}
void solve(int w,int sz){
reset(w,0);
Find(w,0,sz);
par[C] = 0;
dfs(C);
//cout<<"C: "<<C<<" "<<w<<" "<<sz<<endl;
mark[C] = 1;
V.clear();
V.pb(a[C]);
int res = 0;
while(V.size()){
int c = V.back();
V.pp();
if(isc[c])
continue;
if(cnt[c] != occ[c].size()){
res = inf;
break;
}
//cout<<"add: "<<c<<endl;
isc[c] = 1;
res++;
for(auto v:occ[c]){
int cur = v;
while(!isv[cur] and cur){
isv[cur] = 1;
V.pb(a[cur]);
cur = par[cur];
}
}
}
//cout<<"res: "<<res<<endl;
ans = min(ans,res);
//cout<<"----------------------"<<endl;
for(auto u:adj[C]){
if(!mark[u]){
solve(u,subt[u]);
}
}
}
int main(){
//ofstream cout ("out.out");
//ifstream cin ("in.in");
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
cin>>n>>k;
for(int i=1;i<n;i++){
int u,v;
cin>>u>>v;
adj[u].pb(v);
adj[v].pb(u);
}
for(int i=1;i<=n;i++){
cin>>a[i];
occ[a[i]].pb(i);
}
ans = inf;
solve(1,n);
cout<<ans-1<<endl;
}
