using System;
using System.Linq;
using System.Text;
using System.Collections.Generic;
using STR = System.String;
using INT = System.Int32;
using DEC = System.Double;
using BOOL = System.Boolean;
class Program
{
    public static IO IO = new IO();
    static void Main(string[] args)
    {
        INT K = IO.I();
        INT N = IO.I();
        List<INT> memory = new List<INT>();
        List<INT> value = new List<INT>();
        INT count = 0;
        INT target = 0;
        for (INT i = K; i <= N; i++)
        {
            if (PRIME.ISPRIME(i))
            {
                memory.Add(hash(i));
                value.Add(i);
            }
        }
        for (INT i = 0; i < memory.Count; i++)
        {
            List<INT> check = new List<INT>();
            INT j = i;
            for (; j < memory.Count; j++)
            {
                if (check.Contains(memory[j]))
                {
                    break;
                }
                check.Add(memory[j]);
            }
            if (count <= check.Count)
            {
                count = check.Count;
                target = i;
            }
        }
        IO.W(value[target]);
        IO.F();
    }
    static INT hash(INT x)
    {
        if (x >= 10)
        {
            x = hash(hash(x / 10) + x % 10);
        }
        return x;
    }
}
public class PRIME
{
    public static bool ISPRIME(INT p)
    {
        bool f = false;
        if (p == 2) { f = true; }
        else if (p > 2 && (p % 2 != 0))
        {
            f = true;
            INT q = (INT)Math.Sqrt(p);
            for (INT j = 3; j <= q; j += 2) { if (p % j == 0) { f = false; break; } }
        }
        return f;
    }
}
public class IO
{
    private const int WMAX = 1000;
    private StringBuilder SB = new StringBuilder();
    private T R<T>(Func<STR, T> f) { return f(Console.ReadLine()); }
    private T[] R<T>(Func<STR, T> f, char c) { return S().Split(c).Select(f).ToArray(); }
    private T[] R<T>(Func<STR, T> f, INT l) { T[] r = new T[l]; for (INT i = 0; i < l; i++) { r[i] = R(f); } return r; }
    private T[][] R<T>(Func<STR, T> f, INT l, char c) { T[][] r = new T[l][]; for (INT i = 0; i < l; i++) { r[i] = R<T>(f, c); } return r; }
    private void W<T>(Func<T, STR> f, T v, bool lf = true) { SB.Append(f(v)); if (lf) { SB.Append('\n'); } if (SB.Length >= WMAX) { F(); } }
    public STR S() { return R(s => s); }
    public STR[] S(char c) { return R(s => s, c); }
    public STR[] S(INT l) { return R(s => s, l); }
    public STR[][] S(INT l, char c) { return R(s => s, l, c); }
    public INT I() { return R(INT.Parse); }
    public INT[] I(char c) { return R(INT.Parse, c); }
    public INT[] I(INT l) { return R(INT.Parse, l); }
    public INT[][] I(INT l, char c) { return R(INT.Parse, l, c); }
    public DEC D() { return R(DEC.Parse); }
    public DEC[] D(char c) { return R(DEC.Parse, c); }
    public DEC[] D(INT l) { return R(DEC.Parse, l); }
    public DEC[][] D(INT l, char c) { return R(DEC.Parse, l, c); }
    public void W(object s, bool lf = true) { W(v => v.ToString(), s, lf); }
    public void F() { Console.Write(SB); SB.Length = 0; }
}