#include <bits/stdc++.h>
using namespace std;
const int nx=2e5+5, kx=18;
int n, k, u, v, t[nx], lvl[nx], pa[nx][kx], h[nx], vs[nx], rt[nx], sz[nx], ans=INT_MAX;
vector<int> d[nx], c[nx], rv[nx], g[nx];
stack<int> s;
vector<pair<int, int>> edg;
void dfs(int u, int p)
{
lvl[u]=lvl[p]+1;
pa[u][0]=p;
for (int i=1; i<kx; i++) pa[u][i]=pa[pa[u][i-1]][i-1];
for (auto v:d[u]) if (v!=p) dfs(v, u);
}
int lca(int u, int v)
{
if (lvl[u]>lvl[v]) swap(u, v);
for (int i=kx-1; i>=0; i--) if (lvl[pa[v][i]]>=lvl[u]) v=pa[v][i];
if (u==v) return u;
for (int i=kx-1; i>=0; i--) if (pa[u][i]!=pa[v][i]) u=pa[u][i], v=pa[v][i];
return pa[u][0];
}
void dfs1(int u, int p)
{
vs[u]=1;
for (auto v:c[u]) if (v!=p&&!vs[v]) dfs1(v, u);
s.push(u);
}
void dfs2(int u, int p, int hd)
{
vs[u]=1;
rt[u]=hd;
sz[hd]++;
for (auto v:rv[u]) if (v!=p&&!vs[v]) dfs2(v, u, hd);
}
int main()
{
cin.tie(NULL)->sync_with_stdio(false);
cin>>n>>k;
for (int i=1; i<n; i++) cin>>u>>v, d[u].push_back(v), d[v].push_back(u);
for (int i=1; i<=n; i++) cin>>t[i], g[t[i]].push_back(i);
dfs(1, 1);
for (int i=1; i<=k; i++)
{
int hd=g[i][0];
for (auto u:g[i]) hd=lca(hd, u);
h[i]=hd;
}
for (int i=1; i<=n; i++) if (i!=h[t[i]]&&t[pa[i][0]]!=t[i]) c[t[i]].push_back(t[pa[i][0]]), rv[t[pa[i][0]]].push_back(t[i]), edg.push_back({t[i], t[pa[i][0]]}); //cout<<"edge "<<t[i]<<' '<<t[pa[i][0]]<<'\n';
for (int i=1; i<=k; i++) if (!vs[i]) dfs1(i, i);
for (int i=1; i<=k; i++) vs[i]=0;
while (!s.empty())
{
u=s.top();
//cout<<"stack "<<u<<'\n';
s.pop();
if (vs[u]) continue;
dfs2(u, u, u);
}
//for (int i=1; i<=n; i++) cout<<"rt "<<i<<' '<<rt[i]<<'\n';
for (auto [u, v]:edg) if (rt[u]!=rt[v]) sz[u]=1e9;
for (int i=1; i<=k; i++) ans=min(ans, sz[rt[i]]);
cout<<ans-1;
}
