import 'dart:io';

main(List<String> args){
  List numbers = stdin.readLineSync().split(" ").map((n) => int.parse(n)).toList();
  int a=numbers[0];
  int b=numbers[1];
  int c=numbers[2];
  int d=numbers[3];
  bool check=true;
  while(true){
    c-=b;
    if(c<=0){
      check=true;
      break;
    }
    a-=d;
    if(a<=0){
      check=false;
      break;
    }
  }
  print(check?"Yes":"No");
}