let line = readLine()!
let abcd = line.split(separator: " ").map { Int($0)! }
var a = abcd[0]; var b = abcd[1]; var c = abcd[2]; var d = abcd[3]

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