import scala.io.StdIn.readLine
import scala.io.StdIn.readInt

object Main extends App {
    val inp = readLine.split(" ").map(_.toInt)
    val a = inp(0)
    val b = inp(1)
    val c = inp(2)
    val d = inp(3)

    def ceil(a:Long, b:Long): Long = {
        (a+b-1)/b
    }
    if(ceil(c,b)<=ceil(a,d)) print("Yes");
    else print("No");

}