====== 참고 ======

  * http://blog.naver.com/PostView.nhn?blogId=warrenjay83&logNo=30159310699
  * http://jaywix.tistory.com/entry/%ED%81%90%EB%B2%A0%EC%9D%B4%EC%8A%A4-75-%EB%A1%9C-%EC%9D%8C%EC%95%85%EB%A7%8C%EB%93%A4%EA%B8%B0-Tip
  * https://www.youtube.com/watch?v=e1YfEUIPelU