fun main(args: Array<String>){
  var(a,b,c,d) = readLine()!!.split(" ").map{ it.toInt() }
  for(i in 1..101){
  var t = c - b*i
  if(t <= 0){
    println("Yes")
    break
  }
  var s = a - d*i
  if(s <= 0){
    println("No")
    break
  }
  } 
}