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

  val Array(h, w, s, t) = readLine.trim.split(' ').map(_.toLong)
  println(if (h % 2 == 0 || w % 2 == 0) {
    "Yes"
  }else {
    if ((s + t) % 2 == 0) "Yes"
    else "No"
  })
  implicit class Scope[T](val value: T) extends AnyVal {
    @inline
    def let[A](func: T ⇒ A): A = func(value)
  }
}
