object Main extends App {                                                                                                                                      import scala.math.floor
  val sc = new java.util.Scanner (System.in)
  val a = sc.nextInt
  val b = sc.nextInt
  val c = sc.nextInt
  val d = sc.nextInt
  println(if(floor(a/d)<=floor(c/b)) "Yes" else "No")
}