#include <bits/stdc++.h>
#pragma GCC optimize("O3")
using namespace std;
using ll = long long;
#define int ll
vector<vector<int>> adj;
vector<int> p;
vector<bool> rdy;
vector<int> sz;
vector<int> sub;
vector<int> cnt;
vector<int> seen;
vector<int> cityOf;
vector<vector<int>> towns;
int ans;
void dfs(int curr, int prev) {
p[curr] = prev;
sub[curr] = 1;
for(int nxt : adj[curr]) {
if(!rdy[nxt]||nxt==prev) continue;
dfs(nxt,curr);
sub[curr] += sub[nxt];
}
}
int centroid(int curr, int prev, int n) {
for(int nxt : adj[curr]) {
if(!rdy[nxt]||nxt==prev) continue;
if(sub[nxt]>n/2) return centroid(nxt,curr,n);
}
return curr;
}
void solve(int c) {
dfs(c,c);
c = centroid(c,c,sub[c]);
dfs(c,c);
stack<pair<int,int>> s; s.push({c,c});
set<int> reset;
while(!s.empty()) {
auto [curr,prev] = s.top(); s.pop();
cnt[cityOf[curr]]++;
reset.insert(cityOf[curr]);
for(int nxt : adj[curr]) {
if(!rdy[nxt]||nxt==prev) continue;
s.push({nxt,curr});
}
}
int cc = 0;
stack<int> cs;
cs.push(cityOf[c]);
while(!cs.empty()) {
int curr = cs.top(); cs.pop();
if(seen[curr]) continue;
if(cnt[curr]!=sz[curr]) { cc = 1000000000; break; }
seen[curr] = true;
cc++;
for(int t : towns[curr]) {
cs.push(cityOf[p[t]]);
}
}
for(int cty : reset) {
cnt[cty] = 0;
seen[cty] = false;
}
if(ans==-1) ans = cc;
else ans = min(ans,cc);
rdy[c] = false;
for(int nxt : adj[c]) {
if(!rdy[nxt]) continue;
solve(nxt);
}
}
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
ans = -1;
int n,k; cin >> n >> k;
adj.resize(n+1);
p.resize(n+1);
rdy.resize(n+1,true);
sz.resize(k+1);
sub.resize(n+1);
cnt.resize(k+1);
cityOf.resize(n+1);
seen.resize(k+1);
towns.resize(k+1);
for(int i = 0; i < n-1; i++) {
int a,b; cin >> a >> b;
adj[a].push_back(b);
adj[b].push_back(a);
}
for(int i = 1; i <= n; i++) {
cin >> cityOf[i];
sz[cityOf[i]]++;
towns[cityOf[i]].push_back(i);
}
solve(1);
cout << ((ans==1||ans==1000000000)?0:ans-1);
return 0;
}
