#include<algorithm>
#include<bitset>
#include<cmath>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#include<deque>
#include<fstream>
#include<iomanip>
#include<iostream>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<unordered_map>
#include<unordered_set>
#include<utility>
#include<vector>

using namespace std;

#define dbg(x) (cout<<#x<<" = "<<(x)<<'\n')
#ifdef HOME
const string inputFile = "input.txt";
const string outputFile = "output.txt";
#else
const string problemName = "";
const string inputFile = problemName + ".in";
const string outputFile = problemName + ".out";
#endif

typedef long long int lld;
typedef pair<int, int> PII;
typedef pair<int, lld> PIL;
typedef pair<lld, int> PLI;
typedef pair<lld, lld> PLL;

const int INF = (1LL << 31) - 1;
const lld LINF = (1LL << 62) - 1;
const int dx[] = {1, 0, -1, 0, 1, -1, 1, -1};
const int dy[] = {0, 1, 0, -1, 1, -1, -1, 1};
const int MOD = (int)(1e9) + 7;

const int NMAX = 10000 + 5;
const int KMAX = 300 + 5;

int N, K, sol, destination, ok;
vector<int> V[NMAX];
int lvl[NMAX];
int A[KMAX];
int B[KMAX];
bitset<NMAX> viz;

void dfs(int x) {
    if(x == destination) {
        ok = 1;
        return;
    }

    viz[x] = 1;

    for(auto y : V[x]) {
        if(viz[y])
            continue;
        lvl[y] = lvl[x] + 1;
        dfs(y);
        if(ok)
            return;
    }
}

int main() {
    int i, x, y, z, p;

    freopen(inputFile.c_str(), "r", stdin);
    freopen(outputFile.c_str(), "w", stdout);

    scanf("%d%d", &N, &K);

    for(i = 1; i <= K; i++)
        scanf("%d", &A[i]);

    for(i = 1; i <= K; i++)
        scanf("%d", &B[i]);

    for(i = 2; i <= N; i++) {
        scanf("%d%d", &x, &y);
        V[x].push_back(y);
        V[y].push_back(x);
    }

    for(i = 1; i <= K; i++) {
        viz = 0;
        ok = 0;
        destination = B[i];
        lvl[A[i]] = 0;
        dfs(A[i]);
        sol = max(sol, lvl[B[i]]);
    }

    printf("%d", sol);

    return 0;
}