using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Diagnostics;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using Enu = System.Linq.Enumerable;

class Program
{
    void Solve()
    {
        int A = reader.Int(), B = reader.Int();
        var primes = Sieve(B).SkipWhile(x => x < A).ToArray();
        var hash = primes.Select(p => Hash(p)).ToArray();
        int ans = 0, maxCount = 0;

        for (int L = 0; L < hash.Length; L++)
        {
            var set = new HashSet<int>();
            for (int i = L; i < hash.Length; i++)
                if (set.Contains(hash[i])) break;
                else set.Add(hash[i]);
            if (set.Count >= maxCount)
            {
                maxCount = set.Count;
                ans = primes[L];
            }
        }

        Console.WriteLine(ans);
    }

    static List<int> Sieve(int n)
    {
        List<int> primes = new List<int>();
        bool[] composite = new bool[n + 1];
        for (int i = 2; i <= n; i++)
        {
            if (composite[i]) continue;
            primes.Add(i);
            for (int j = i + i; j <= n; j += i) composite[j] = true;
        }
        return primes;
    }

    int Hash(int n)
    {
        int hash = 0;
        while (n > 0) { hash += n % 10; n /= 10; }
        if (hash >= 10) return Hash(hash);
        return hash;
    }



    Reader reader = new Reader(Console.In);
    static void Main() { new Program().Solve(); }
}

class Reader
{
    private readonly TextReader reader;
    private readonly char[] separator = { ' ' };
    private readonly StringSplitOptions removeOp = StringSplitOptions.RemoveEmptyEntries;
    private string[] A = new string[0];
    private int i;

    public Reader(TextReader r) { reader = r; }
    public bool HasNext() { return Enqueue(); }
    public string String() { return Dequeue(); }
    public int Int() { return int.Parse(Dequeue()); }
    public long Long() { return long.Parse(Dequeue()); }
    public double Double() { return double.Parse(Dequeue()); }
    public int[] IntLine() { var s = Line(); return s == "" ? new int[0] : Array.ConvertAll(Split(s), int.Parse); }
    public int[] IntArray(int N) { return Enu.Range(0, N).Select(i => Int()).ToArray(); }
    public int[][] IntGrid(int H) { return Enu.Range(0, H).Select(i => IntLine()).ToArray(); }
    public string[] StringArray(int N) { return Enu.Range(0, N).Select(i => Line()).ToArray(); }
    public string Line() { return reader.ReadLine().Trim(); }
    private string[] Split(string s) { return s.Split(separator, removeOp); }
    private bool Enqueue()
    {
        if (i < A.Length) return true;
        string line = reader.ReadLine();
        if (line == null) return false;
        if (line == "") return Enqueue();
        A = Split(line);
        i = 0;
        return true;
    }
    private string Dequeue() { Enqueue(); return A[i++]; }
}