using System;
using System.Collections.Generic;
using System.Linq;

namespace yukicoder
{
	public class Program
	{
		public static void Main()
		{
			var a = Console.ReadLine().Trim().Split(' ').Select(value => fs(int.Parse(value))).Distinct().ToArray();
			var k = Math.Max(a[0], a[1]);
			Console.WriteLine(fs(k));
		}
		static int fs(int a)
        {
			var k = a.ToString();
			var A = "";
			foreach(var s in k)
            {
                if (s == '7')
                {
					A += "4";
                }
				else if (s == '4')
                {
					A += "7";
                }
                else
                {
					A += s;
                }
            }
			a = int.Parse(A);
			return a;
        }
	}
}