#include <cstdio>
#include <algorithm>
#include <cstring>
#include <vector>

using namespace std;

#define maxs 310
#define maxn 10010

int n, k;
int p[maxs], s[maxs];
int f[maxn], d[maxs][maxn];
int cuplaj[maxn], cuplaj2[maxn], viz[maxn];
vector<int> v[maxn];

void df(int nod, int lvl, int dd)
{
    if(f[nod])
        return;

    f[nod]=1;
    d[lvl][nod]=dd;

    for(int i=0; i<v[nod].size(); ++i)
        if(f[v[nod][i]]==0)
            df(v[nod][i], lvl, dd+1);
}

int cupleaza(int nod)
{
    int vecin, i;
    if(viz[nod])
        return 0;
    viz[nod]=1;
    for(i=0; i<v[nod].size(); i++)
    {
        vecin=v[nod][i];
        if(!cuplaj[vecin])
        {
            cuplaj2[nod]=1;
            cuplaj[vecin]=nod;
            return 1;
        }
    }
    for(i=0; i<v[nod].size(); i++)
    {
        vecin=v[nod][i];
        if(cuplaj[vecin]!=nod)
        if(cupleaza(cuplaj[vecin]))
        {
            cuplaj2[nod]=1;
            cuplaj[vecin]=nod;
            return 1;
        }
    }
    return 0;
}

int solve(int med)
{
    for(int i=1; i<=k; ++i)
        v[i].clear();

    for(int i=1; i<=k; ++i)
        for(int j=1; j<=k; ++j)
            if(d[i][s[j]]<=med)
                v[i].push_back(j);

    memset(cuplaj, 0, sizeof(cuplaj));
    memset(cuplaj2, 0, sizeof(cuplaj2));

    int ok=1, sol=0;
    while(ok)
    {
        ok=0;
        memset(viz, 0, sizeof(viz));
        for(int i=1; i<=k; ++i)
        {
            if(!cuplaj2[i])
            if(cupleaza(i))
            {
                sol++;
                ok=1;
            }
        }
    }

    if(sol==k)
        return 1;
    return 0;
}

int main()
{
  //  freopen("kspecialists.in", "r", stdin);

    scanf("%d%d", &n, &k);

    for(int i=1; i<=k; ++i)
        scanf("%d", &p[i]);

    for(int i=1; i<=k; ++i)
        scanf("%d", &s[i]);

    for(int i=1; i<n; ++i)
    {
        int a, b;
        scanf("%d%d", &a, &b);
        v[a].push_back(b);
        v[b].push_back(a);
    }

    for(int i=1; i<=k; ++i)
    {
        memset(f, 0, sizeof(f));

        df(p[i], i, 0);
    }

    int left=1, sol=n, right=n;

    while(left<=right)
    {
        int med=(left+right)/2;
        if(solve(med))
        {
            sol=med;
            right=med-1;
        }
        else
            left=med+1;
    }

    printf("%d\n", sol);

    return 0;
}