import Foundation

let N = readLine()!.components(separatedBy:" ").map{Int($0)!}
var A = N[2] / N[1]
let a = N[2] % N[1]
var B = N[0] / N[3]
let b = N[0] % N[3]
if(a > 0){
  A += 1
}
if(b > 0){
  B += 1
}
if(A <= B){
  print("Yes")
}else{
  print("No")
}