import Foundation
var str = readLine()!.components(separatedBy:" ")
var a = Int(str[0])!
var b = Int(str[1])!
var c = Int(str[2])!
var d = Int(str[3])!
var ans = ""

while true {
  c = c-b
  if c<=0{
    ans = "Yes"
    break
  }
  a = a-d
  if a<=0{
    ans = "No"
    break
  }
}
print(ans)