let arr=readLine()!.split{$0==" "}.map{Int(String($0))!}
var a=arr[0]
var b=arr[1]
var c=arr[2]
var d=arr[3]
 
while(true){
    
    c -= b
    if c <= 0 {
          print("Yes")
          break
      }
    a -= d
    if a <= 0 {
        print("No")
        break
    }
}