https://hashcode.co.kr/questions/2100/intent%EB%A1%9C-%EA%B2%80%EC%83%89%EC%9D%B4-%EB%90%98%EC%9E%88%EB%8A%94-%EA%B5%AC%EA%B8%80%EC%B0%BD%EC%9D%84-%EB%9D%84%EC%9A%B0%EA%B8%B0-%EA%B0%80%EB%8A%A5%ED%95%9C%EA%B0%80%EC%9A%94