import java.util.Scanner

import scala.annotation.tailrec
import scala.io.StdIn._

object Main extends App {

  val Array(a,b,c,d) = readLine().split(" ").map(_.toInt)

  def solve() = {
    val aAtkCount = ceil(a,d)
    val tAtkCount = ceil(c,b)
    if(tAtkCount <= aAtkCount) "Yes" else "No"
  }

  def ceil(a: Int, b: Int): Int = (a+b-1)/b

  println(solve())

}

