#include <iostream>
#include <vector>
#include <queue>
#define INF 1000000000
using namespace std;
int n, K, spec[310], oras[310], dist[310][310];
vector <int> G[10100];
bool viz[310], permis[310][310];
int A[310], B[310];

void BFS(int ind)
{
	queue <int> Q;
	int i, x, best[10100];
	vector <int>::iterator it;
	for(i = 1; i <= n; ++i)
		best[i] = INF;
	best[spec[ind]] = 0;
	Q.push(spec[ind]);
	while(!Q.empty())
	{
		x = Q.front();
		Q.pop();
		for(it = G[x].begin(); it != G[x].end(); ++it)
		{
			if(best[*it] > best[x] + 1)
			{
				best[*it] = best[x] + 1;
				Q.push(*it);
			}
		}
	}
	for(i = 1; i <= K; ++i)
		dist[ind][i] = best[oras[i]];
}

bool HopcroftKarp(int x)
{
	if(viz[x])
		return false;
	int i;
	viz[x] = true;
	for(i = 1; i <= K; ++i)
	{
		if(permis[x][i] && !A[i])
		{
			A[i] = x;
			B[x] = i;
			return true;
		}
	}
	for(i = 1; i <= K; ++i)
	{
		if(permis[x][i] && HopcroftKarp(A[i]))
		{
			A[i] = x;
			B[x] = i;
			return true;
		}
	}
	return false;
}

bool Bun(int maxim)
{
	int i, j;
	bool modif = true;
	for(i = 1; i <= K; ++i)
		A[i] = B[i] = 0;
	for(i = 1; i <= K; ++i)
		for(j = 1; j <= K; ++j)
		{
			if(dist[i][j] <= maxim)
				permis[i][j] = true;
			else
				permis[i][j] = false;
		}
	while(modif)
	{
		modif = false;
		for(i = 1; i <= K; ++i)
			viz[i] = false;
		for(i = 1; i <= K; ++i)
			if(!B[i])
				modif |= HopcroftKarp(i);
	}
	for(i = 1; i <= K; ++i)
		if(!B[i])
			return false;
	return true;
}

int BinarySearch()
{
	int st, dr, mij, rez;
	st = 0;
	dr = rez = 2 * n;
	while(st <= dr)
	{
		mij = (st + dr) / 2;
		if(Bun(mij))
		{
			rez = mij;
			dr = mij - 1;
		}
		else
			st = mij + 1;
	}
	return rez;
}

int main()
{
	int i, x, y;
	cin >> n >> K;
	for(i = 1; i <= K; ++i)
		cin >> spec[i];
	for(i = 1; i <= K; ++i)
		cin >> oras[i];
	for(i = 1; i < n; ++i)
	{
		cin >> x >> y;
		G[x].push_back(y);
		G[y].push_back(x);
	}
	
	for(i = 1; i <= K; ++i)
		BFS(i);
	cout << BinarySearch() << "\n";
	return 0;
}