import java.util.Scanner

object Problem293 {

  def keta(a: Int): Int = a.toString.length

  def max(a: Int, b: Int): Int = {
    if (keta(a) != keta(b)) {
      return a max b
    }

    val sa = a.toString
    val sb = b.toString

    (0 until sa.length) foreach { i =>
      val ca = sa(i) - '0'
      val cb = sb(i) - '0'

      (ca, cb) match {
        case (4, 7) => return a
        case (7, 4) => return b
        case _ if ca != cb => return a max b
        case _ => // eq
      }
    }

    // 同じ
    a
  }

  def main(args: Array[String]) = {
    val sc = new Scanner(System.in)
    val a = sc.nextInt()
    val b = sc.nextInt()

    val result = max(a, b)
    println(result)
  }
}