import scala.io.StdIn._
object Main {
  def main(args:Array[String]) ={
    val read = readLine().split(' ').map(_.toInt)

    var Tturn = read(2) / read(1)
    if(read(2) % read(1) != 0) Tturn += 1
    var Aturn = read(0) / read(3)
    if(read(0) % read(3) != 0) Aturn += 1
    
    if(Tturn <= Aturn) println("Yes")
    else println("No")
  }
}