#include <iostream>
#include <vector>
#include <queue>
#define ll long long
using namespace std;
vector <ll> adj[200000];
bool C[200000];
vector <ll> V[200000];
ll n, k, a, b, cnt, f = 1e18, A[200000], B[200000], sz[200000], P[200000], visited[200000], G[200000];
void dfs_sz(ll u, ll p) {
B[u] = cnt;
sz[u] = 1;
for (auto v : adj[u]) {
if (v != p && !C[v]) {
dfs_sz(v, u);
sz[u] += sz[v];
}
}
}
ll find_cent(ll u, ll p, ll tot) {
ll mx = -1, ret = -1;
for (auto v : adj[u]) {
if (v != p && !C[v]) {
ret = max(ret, find_cent(v, u, tot));
mx = max(mx, sz[v]);
}
}
mx = max(mx, tot-sz[u]);
if (mx <= tot/2) return u;
else return ret;
}
void dfs_par(ll u, ll p) {
for (auto v : adj[u]) {
if (v != p && !C[v]) {
dfs_par(v, u);
P[v] = u;
}
}
}
void solve(ll u) {
ll cur = 0;
++cnt;
dfs_sz(u, -1);
ll cent = find_cent(u, -1, sz[u]);
C[cent] = 1;
dfs_par(cent, -1);
queue <ll> Q;
bool ok = 1;
G[A[cent]] = cnt;
Q.push(A[cent]);
while (!Q.empty()) {
auto g = Q.front();
Q.pop();
++cur;
for (auto v : V[g]) {
if (B[v] != cnt) {
ok = 0;
break;
}
ll x = v;
while (visited[x] != cnt) {
if (G[A[x]] != cnt) {
G[A[x]] = cnt;
Q.push(A[x]);
}
visited[x] = cnt;
if (x == cent) break;
x = P[x];
}
}
if (!ok) break;
}
if (ok) f = min(f, cur);
for (auto v : adj[cent]) {
if (!C[v]) solve(v);
}
}
int main() {
cin >> n >> k;
for (int i=0; i<n-1; ++i) {
cin >> a >> b;
--a, --b;
adj[a].push_back(b);
adj[b].push_back(a);
}
for (int i=0; i<n; ++i) {
G[i] = -1;
visited[i] = -1;
cin >> A[i];
--A[i];
V[A[i]].push_back(i);
}
solve(0);
cout << f-1 << '\n';
}
