import java.io.{BufferedOutputStream, BufferedReader, InputStreamReader, PrintWriter}

object Main {
  def main(args: Array[String]): Unit = {
    val in = new BufferedReader(new InputStreamReader(System.in))
    val out = new PrintWriter(new BufferedOutputStream(System.out))
    var Array(a, b, c, d) = in.readLine().split("\\s+").map(_.toInt)

    while (true) {
      c -= b
      if (c <= 0) {
        out.println("Yes")
        out.flush()
        return
      }
      a -= d
      if (a <= 0) {
        out.println("No")
        out.flush()
        return
      }
    }
  }
}
