Add elements to an Akka Streams dynamically and accumulate them in batches

DynamicBatchedSource.scala

import akka.actor.ActorSystem
import akka.stream.scaladsl.{Flow, Sink, Source}
import akka.stream.{ActorMaterializer, OverflowStrategy}

import scala.concurrent.duration._
import scala.io.StdIn

object DynamicBatchedSource extends App {

  implicit val system: ActorSystem = ActorSystem("QuickStart")
  implicit val materializer: ActorMaterializer = ActorMaterializer()

  val queue = Source
    .queue[Int](100, OverflowStrategy.fail)
    .to(
      Flow[Int]
        .groupedWithin(5, 20 seconds)
        .to(Sink foreach println))
    .run

  println("Enter number")

  while (true) {
    queue offer StdIn.readInt()
  }
}