import java.util.*

fun main(args: Array<String>) {
    val scanner = Scanner(System.`in`)
    var takaHP = scanner.nextInt()
    val takaAT = scanner.nextInt()
    var aoHP = scanner.nextInt()
    val aoAT = scanner.nextInt()
    var check = true
    do{
        if(check) {
            aoHP -= takaAT
            check = false
        }
        else {
            takaHP -= aoAT
            check = true
        }

    }while (takaHP > 0 && aoHP > 0)
    if(aoHP <= 0) println("Yes")
    else println("No")

}