import Foundation

let input_line: String = readLine()!
let split: [String] = input_line.components(separatedBy: " ") //ブランクで区切られている場合

var a = Int(split[0])!
let b = Int(split[1])!
var c = Int(split[2])!
let d = Int(split[3])!


var ans = "Yes"

var ta = 0

while ta >= 0 {
    a -= d
  if a <= 0 { break }
    ta += 1
}

var ao = 0

while ao >= 0 {
    c -= b
  if  c <= 0 { break }
    ao += 1
}

if ao > ta {
    ans = "No"
}


print(ans)