object Main extends App {
  import scala.io.StdIn._

  val n = readInt
  val line1 = readLine.trim.split(' ').map(_.toInt)
  val line2 = readLine.trim.split(' ').map(_.toInt)
  for (i ← line1.indices.tail) line1(i) += line1(i - 1)
  for (i ← line2.indices.reverse.tail) line2(i) += line2(i + 1)
  println(
    line1.zip(line2).map{case (a, b) ⇒ a + b}.max
  )
}