import scala.io.StdIn.readLine

def solve() = {
  val s = readLine.split(" ").map(x => x.toInt)
  var a = s(0)
  val b = s(1)
  var c = s(2)
  val d = s(3)
  while (true) {
    c -= b
    if (c <= 0) {
      println("Yes")
      return
    }
    a -= d
    if (a <= 0) {
      println("No")
      return
    }
  }
}

object Main extends App {
  solve()
}
