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() = {
    var tLife = a
    val tAtk = b
    var aLife = c
    val aAtk = d

    var tTurn = true
    while(tLife > 0 && aLife > 0) {
      if(tTurn) aLife -= tAtk
      else tLife -= aAtk
      tTurn = !tTurn
    }
    if(tLife <= 0) "No" else "Yes"
  }

  println(solve())

}

