// #pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define int long long
vector<int> adj[200001];
bool processed[200001];
int siz[200001];
bool current[200001];
int par[200001];
int visitedcol[200001];
int col[200001];
vector<int> nodes[200001];
void set_all(int x,int p,bool set_val){
if(processed[x])return;
current[x] = set_val;
par[x] = p;
for(int&i:adj[x])if(i!=p)set_all(i,x,set_val);
}
int cnt(int x,int p){
if(processed[x])return 0;
int ans = 1;
for(int&i:adj[x])if(i!=p)ans+=cnt(i,x);
return ans;
}
int centroid;
int centroidcalc(int x,int p,int tot){
if(processed[x])return 0;
siz[x] = 1;
bool works = true;
for(int&i:adj[x])if(i!=p){
int res = centroidcalc(i,x,tot);
siz[x]+=res;
if(res>tot/2)works=false;
}
if(tot-siz[x]>tot/2)works=false;
if(works){
centroid = x;
return 1e15;
}
return siz[x];
}
int calc(int x){
centroidcalc(x,0,cnt(x,0));
set_all(centroid,0,true); // Get them into processing stage
queue<int> q; // Queue of colours
q.emplace(col[centroid]);
int ans = -1;
while(!q.empty()){
int curr = q.front();q.pop();
if(visitedcol[curr]==centroid)continue;
visitedcol[curr]=centroid;
ans++;
for(int&i:nodes[curr]){
if(!current[i]){
while(!q.empty())q.pop();
ans = 1e15;
break;
}
if(par[i])q.emplace(col[par[i]]);
}
}
set_all(centroid,0,false);
processed[centroid]=true;
for(int&i:adj[centroid])if(!processed[i])ans=min(ans,calc(i));
return ans;
}
int32_t main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n,k;
cin >> n >> k;
for(int i=1;i<n;i++){
int a,b;cin>>a>>b;
adj[a].emplace_back(b);
adj[b].emplace_back(a);
}
for(int i=1;i<=n;i++){
cin>>col[i];
nodes[col[i]].emplace_back(i);
}
siz[1]=n;
cout << calc(1) << '\n';
}
