#include <iostream>
#include<vector>
#include<queue>
#include<map>
#include<string>
#include<cstring>
#include<iomanip>
#include<algorithm>
#include<cmath>
#include<set>
#include<stack>
#include<sstream>
using namespace std;
vector<vector<int> > g(1024);
vector<int> distForFastestDrop(1024, 1000000000);

void bfs(int source){
vector<bool> visited(1024);
    queue<pair<int, int> > q;
    vector<int> dist(1024, 1000000000);
    q.push(make_pair(source, 0));
    visited[source] = true;
    while(!q.empty()){
        pair<int, int> f = q.front();
        int v = f.first;
        int d = f.second;
        dist[v] = min(dist[v], d);
       // cout << v << " " << d << endl;
        q.pop();
        for(int i = 0; i < g[v].size(); i++){
            int inV = g[v][i];
            if(!visited[inV]){
                q.push(make_pair(inV, d+1));
                visited[inV] = true;
            }
        }
    }

    for(int i = 0; i < 1024; i++){
        distForFastestDrop[i] = min(distForFastestDrop[i], dist[i]);
    }
}
int main()
{
    int n, k;
    cin >> n >> k;
    vector<int> specs(k);
    vector<int> servers(k);
    for(int i = 0; i < k; i++){
            cin >> specs[i];
    }

    for(int i = 0; i < k; i++){
            cin >> servers[i];
    }

    for(int i = 0; i < n -1; i++){
            int x,y;
        cin >> x >> y;
        g[x].push_back(y);
        g[y].push_back(x);
    }

    for(int i = 0; i < specs.size(); i++){
            //cout <<"sp " << specs[i] << endl;
        bfs(specs[i]);
    }

    int max1 = -1;
    for(int i = 0; i < servers.size(); i++){
       // cout << distForFastestDrop[servers[i]] << endl;
        max1 = max(max1, distForFastestDrop[servers[i]]);
    }

    cout << max1 << endl;
    return 0;
}