#include<cstdio>
#include<queue>
#include<vector>
#include<cstring>
using namespace std;
#define NMAX 10005
queue <int> q;
vector <int> G[NMAX];
int n,m,s,x,y,sol,Nr[NMAX],a[NMAX],b[NMAX];
void citire()
{
    int i;
    scanf("%d%d",&n,&m);
    memset(Nr,0x3f,sizeof(Nr));
    for (i=1;i<=m;++i)
    {
        scanf("%d",&a[i]);
        q.push(a[i]);
        Nr[a[i]]=1;
    }
    for (i=1;i<=m;++i)
        scanf("%d",&b[i]);
    for (i=1;i<n;++i)
        scanf("%d%d",&x,&y), G[x].push_back(y), G[y].push_back(x);
}
void bfs()
{
    int i;
    while (!q.empty())
    {
        x=q.front(); q.pop();
        for (i=0;i<G[x].size();++i)
        {
            y=G[x][i];
            if (Nr[y]>Nr[x]+1)
            {
                q.push(y);
                Nr[y]=Nr[x]+1;
            }
        }
    }
}
int main()
{
    int i;
//    freopen("date.in","r",stdin);
//    freopen("date.out","w",stdout);
    citire();
    bfs();
    sol=Nr[b[1]]-1;
    for (i=2;i<=m;++i)
    {
        sol=max(sol,Nr[b[i]]-1);
    }
    printf("%d",sol);
    printf("\n");
    return 0;
}