import java.util.Scanner

object Main {
  def main(args: Array[String]): Unit = {
    //nextLineとnextを同時に使ったら死ぬ
    val sc = new Scanner(System.in)
    val a, b, c, d = sc.nextInt()
    val aa = if (a % d == 0) a / d else a / d + 1
    val cc = if (c % b == 0) c / b else c / b + 1

    if (aa >= cc) {
      println("Yes")
    } else {
      println("No")
    }
  }
}
