import java.util.Scanner
import scala.util.control.Breaks._


object Main {
  def main(args:Array[String]) = {
    val sc = new java.util.Scanner(System.in)
    var TM_HP: Long = sc.nextLong
    var TM_AT: Long = sc.nextLong
    var AM_HP: Long = sc.nextLong
    var AM_AT: Long = sc.nextLong
    
    breakable {
    	while(true) {
            AM_HP = AM_HP - TM_AT
            if( AM_HP < 1){
              println("Yes")
              break
            }
            
            TM_HP = TM_HP - AM_AT
            if( TM_HP < 1){
              println("No")
              break
            } 
    	    
    	}
    }


    
  }
}