import java.io.*;
import java.util.ArrayList;
import java.util.StringTokenizer;
import java.util.Vector;

final public class Main
{

    public static ArrayList<ArrayList<Integer>> adjacencyList = new ArrayList<>();
    public static int[] distances;
    public static boolean[] isVisited;
    public static int n;
    public static int ex = 0;
    public static int diam = 0;
    public static int node = -1;
    public static int numberOfVisited = 0;
    public static Vector<Integer> queue = new Vector<>();


    public static void bfs(int s)
    {
        queue.add(s);
        distances[s] = 0;
        isVisited[s] = true;
        ex = 0;
        numberOfVisited = 1;
        while (!queue.isEmpty())
        {
            int v = queue.remove(0);
            for (Integer i : adjacencyList.get(v))
            {
                if (!isVisited[i])
                {
                    queue.add(i);
                    distances[i] = distances[v] + 1;
                    isVisited[i] = true;
                    numberOfVisited++;
                    if (distances[i] > ex)
                    {
                        ex = distances[i];
                    }
                }
            }
        }
    }

    public static void check(int currNode)
    {
        if (numberOfVisited == n)
        {
            if (ex > diam)
            {
                diam = ex;
                node = currNode;
            }
        }
    }

    public static void update()
    {
        for (int i = 0;i < n; i++)
        {
            isVisited[i] = false;
        }
    }

    public static void solve()
    {
        for (int i = 0;i < n;i++)
        {
            bfs(i);
            check(i);
            update();
        }
    }

    public static void read(String inputPath) throws IOException
    {
        BufferedReader bf = new BufferedReader(new FileReader(inputPath));
        n = Integer.parseInt(bf.readLine());
        for (int i = 0;i < n;i++)
        {
            adjacencyList.add(new ArrayList<>());
        }
        distances = new int[n];
        isVisited = new boolean[n];
        String line;
        int count = 0;
        while((line = bf.readLine()) != null)
        {
            StringTokenizer st = new StringTokenizer(line," \t\r\n");
            st.nextToken();
            while(st.hasMoreTokens())
            {
                adjacencyList.get(count).add(Integer.parseInt(st.nextToken())-1);
            }
            count++;
        }
    }

    public static void show()
    {
        for (int i = 0;i < n;i++)
        {
            System.out.println(i + " ->  " + adjacencyList.get(i));
        }
    }

    public static void main(String[] args) throws IOException
    {
        read("in.txt");
        solve();
        PrintWriter pr = new PrintWriter(new File("out.txt"));
        if(node != -1)
        {
            pr.print(diam + "\n");
            pr.print(node + 1);
        }
        else
        {
            pr.print("impossible");
        }
        pr.flush();

    }
}