import java.util.Arrays;
import java.util.InputMismatchException;
import java.util.ArrayList;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.IOException;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 * @author George Marcus
 */
public class prog {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		kspecialists solver = new kspecialists();
		solver.solve(1, in, out);
		out.close();
	}
}

class kspecialists {
    int[] specNode;
    int[] serverInNode;
    ArrayList<Integer>[] A;
    int[][] D;
    int[] left;
    int[] right;
    boolean[] v;
    int K;
    int U;

    public void solve(int testNumber, InputReader in, PrintWriter out) {
        int N = in.nextInt();
        K = in.nextInt();
        specNode = new int[N];
        serverInNode = new int[N];
        for (int i = 0; i < K; i++) {
            int a = in.nextInt();
            a--;
            specNode[i] = a;
        }
        Arrays.fill(serverInNode, -1);
        for (int i = 0; i < K; i++) {
            int b = in.nextInt();
            b--;
            serverInNode[b] = i;
        }

        A = new ArrayList[N];
        for (int i = 0; i < N; i++) {
            A[i] = new ArrayList<Integer>();
        }
        for (int i = 0; i < N - 1; i++) {
            int a = in.nextInt() - 1;
            int b = in.nextInt() - 1;
            A[a].add(b);
            A[b].add(a);
        }

        D = new int[K][K];
        for (int i = 0; i < K; i++) {
            dfs(specNode[i], -1, 0, D[i]);
        }

        left = new int[K];
        right = new int[K];
        v = new boolean[K];

        int st = 0;
        int dr = N;
        int m = -1;
        int ans = -1;
        while (st <= dr) {
            m = (st + dr) / 2;
            if (match(m) == K) {
                ans = m;
                dr = m - 1;
            }
            else {
                st = m + 1;
            }
        }

        out.println(ans);
    }

    private int match(int upper) {
        Arrays.fill(left, -1);
        Arrays.fill(right, -1);
        Arrays.fill(v, false);

        U = upper;
        int ret = 0;
        boolean ok = true;
        while (ok) {
            ok = false;
            Arrays.fill(v, false);
            for (int i = 0; i < K; i++) {
                if (right[i] == -1 && pairup(i)) {
                    ret++;
                    ok = true;
                }
            }
        }

        return ret;
    }

    private boolean pairup(int node) {
        if (v[node]) {
            return false;
        }
        v[node] = true;

        for (int i = 0; i < K; i++) {
            if (D[node][i] <= U) {
                if (left[i] == -1) {
                    left[i] = node;
                    right[node] = i;
                    return true;
                }
            }
        }

        for (int i = 0; i < K; i++) {
            if (D[node][i] <= U) {
                if (pairup(left[i])) {
                    left[i] = node;
                    right[node] = i;
                    return true;
                }
            }
        }

        return false;
    }

    private void dfs(int node, int prev, int dist, int[] D) {
        if (serverInNode[node] != -1) {
            D[ serverInNode[node] ] = dist;
        }
        for (int x : A[node]) {
            if (x != prev) {
                dfs(x, node, dist + 1, D);
            }
        }
    }
}

class InputReader {
    private InputStream stream;
    private byte[] buf = new byte[1024];
    private int curChar;
    private int numChars;

    public InputReader(InputStream stream) {
        this.stream = stream;
    }

    public int read() {
        if (numChars == -1)
            throw new InputMismatchException();
        if (curChar >= numChars) {
            curChar = 0;
            try {
                numChars = stream.read(buf);
            } catch (IOException e) {
                throw new InputMismatchException();
            }
            if (numChars <= 0)
                return -1;
        }
        return buf[curChar++];
    }

    public int nextInt() {
        return Integer.parseInt(nextString());
    }

    public String nextString() {
        int c = read();
        while (isSpaceChar(c))
            c = read();
        StringBuffer res = new StringBuffer();
        do {
            res.appendCodePoint(c);
            c = read();
        } while (!isSpaceChar(c));

        return res.toString();
    }

    private boolean isSpaceChar(int c) {
        return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
    }

}