/*
    There's no such thing as a limit on being the best.
    You can always go for more.
    That's what it means to be human.
    No... That's what it means to be me.
*/

#include<fstream>
#include<iostream>
#include<cstdio>
#include<map>
#include<set>
#define FIT(a,b) for(vector<int >::iterator a=b.begin();a!=b.end();a++)
#define FITP(a,b) for(vector<pair<int,int> >::iterator a=b.begin();a!=b.end();a++)
#define RIT(a,b) for(vector<int>::reverse_iterator a=b.end();a!=b.begin();++a)
#include<stack>
#define ROF(a,b,c) for(int a=b;a>=c;--a)
#include<vector>
#include<algorithm>
#define FOR(a,b,c) for(int a=b;a<=c;++a)
#define REP(a,b) for(register int a=0;a<b;++a)
#include<cstring>
#include<bitset>
#include<cmath>
#include<iomanip>
#include<set>
#define f cin
#define g cout
#include<queue>
#define debug cerr<<"OK";
#define pii pair<int,int>
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define ll long long
#define ull unsigned long long
#define mod 1000000007
#define N 100100
#define K 310
#define SQR 350
#define inf 1<<30
#define div pula
#define hi pizda
#define down haha
using namespace std;
/*int dx[]={0,0,0,1,-1};
int dy[]={0,1,-1,0,0};*/

queue<int> q;
vector<int> h[N], v[N];
priority_queue<pii > pq[K];
int spe[N],n,k,sol,tak[N],viz[N],x,serv[N],y,ser[N],sp[N];

void bfs(int x)
{
    int ind=x;
    x=serv[x];
    memset(viz,0,sizeof(viz));
    viz[x]=1;
    while(!q.empty())
        q.pop();
    q.push(x);
    while(!q.empty())
    {
        x=q.front();
        q.pop();
        FIT(it,v[x])
        if(!viz[*it])
        {
            viz[*it]=viz[x]+1;
            if(sp[*it])
            {
                FIT(it2,h[*it])
                pq[ind].push(mp(-viz[*it]+1,*it2));
            }
            q.push(*it);
        }
    }
}
int main ()
{
    #ifndef ONLINE_JUDGE
    freopen("a.in","r",stdin);
    freopen("a.out","w",stdout);
    #endif

    f>>n>>k;

    FOR(i,1,k)
    {
        f>>x;
        sp[x]=1;
        h[x].pb(i);
    }
    FOR(i,1,k)
    {
        f>>x;
        serv[i]=x;
        ser[x]=1;
    }
    FOR(i,1,n-1)
    {
        f>>x>>y;
        v[x].pb(y);
        v[y].pb(x);
    }
    FOR(i,1,k)
        bfs(i);
    memset(viz,0,sizeof(viz));
    FOR(i,1,k)
    {
        FOR(j,1,k)
        {
            if(tak[j])
                continue;
            while(viz[pq[j].top().se])
                pq[j].pop();
        }
        int be=0;
        int cant=-n;
        FOR(j,1,k)
        {
            if(tak[j])
                continue;
            if(pq[j].top().fi>cant)
            {
                cant=pq[j].top().fi;
                be=j;
            }
        }
        sol=max(sol,-cant);
        viz[pq[be].top().se]=1;
        tak[be]=1;
    }
    g<<sol;
    return 0;
}