import 'dart:io';

main(List<String> args) {
  List ABCD = stdin.readLineSync().split(' ').map((x) => int.parse(x)).toList();
  if (ABCD[0] ~/ ABCD[3] < ABCD[2] ~/ ABCD[1])
    print("Yes");
  else
    print("No");
}
