class Program
{
    static void Main(string[] args)
    {
        string[] num = Console.ReadLine().Split(' ');
        string numA = num[0];
        string numB = num[1];
        string ans = "";
        if(numA.Length > numB.Length)
        {
            ans = numA;
        }else if(numB.Length > numA.Length)
        {
            ans = numB;
        }
        else
        {
            for(int i = 0; i < numA.Length; i++)
            {
                if (numA[i] == '4' && numB[i] == '7')
                {
                    ans = numA;
                }else if (numA[i] == '7' && numB[i] == '4')
                {
                    ans = numB;
                }
                else if (int.Parse(numA[i].ToString()) > int.Parse(numB[i].ToString())){
                    ans = numA;
                }
                else if (int.Parse(numB[i].ToString()) > int.Parse(numA[i].ToString()))
                {
                    ans = numB;
                }
                if (ans != "")
                {
                    break;
                }
            }
        }
        Console.WriteLine(ans);
    }
}