module Yuki

open System

let solve a b =
    let swap4and7 =
        string
        >> fun x -> x.Replace('4', 't')
        >> fun x -> x.Replace('7', '4')
        >> fun x -> x.Replace('t', '7')
        >> int64
    let a' = swap4and7 a
    let b' = swap4and7 b
    if a' > b' then a
    else b

let A, B = 
    let t = 
        Console.ReadLine().Split() 
        |> Array.map int64
    t.[0], t.[1]

solve A B
|> Console.WriteLine