using System;

namespace No293{
    public class Program{
        public static void Main(string[] args){
            var sr = new StreamReader();
            //---------------------------------
            var A = sr.Next<int>();
            var B = sr.Next<int>();

            if(A.ToString().Length > B.ToString().Length){
                Console.WriteLine(A);
                return;
            }
            if(A.ToString().Length < B.ToString().Length){
                Console.WriteLine(B);
                return;
            }

            for(var i = 0; i < A.ToString().Length; i++){
                if(A.ToString()[i] == '4' && B.ToString()[i] == '7') {
                    Console.WriteLine(A);
                    return;
                }
                if(A.ToString()[i] == '7' && B.ToString()[i] == '4') {
                    Console.WriteLine(B);
                    return;
                }
                if(A.ToString()[i] > B.ToString()[i]){
                    Console.WriteLine(A);
                    return;
                }
                if(A.ToString()[i] < B.ToString()[i]) {
                    Console.WriteLine(B);
                    return;
                }
            }
            //---------------------------------
        }
    }

    public class StreamReader{
        private readonly char[] _c = {' '};
        private int _index = -1;
        private string[] _input = new string[0];

        public T Next<T>(){
            if(_index == _input.Length - 1){
                _index = -1;
                while(true){
                    string rl = Console.ReadLine();
                    if(rl == null){
                        if(typeof(T).IsClass) return default(T);
                        return (T)typeof(T).GetField("MinValue").GetValue(null);
                    }
                    if(rl != ""){
                        _input = rl.Split(_c, StringSplitOptions.RemoveEmptyEntries);
                        break;
                    }
                }
            }
            return (T)Convert.ChangeType(_input[++_index], typeof(T), System.Globalization.CultureInfo.InvariantCulture);
        }
    }
}