Watchers

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  Gene McGahey

  https://edukr.net/%ED%86%A0%ED%86%A0%EC%82%AC%EC%9D%B4%ED%8A%B8-%EA%B0%80%EC%9E%85%EC%BD%94%EB%93%9C%EC%9D%98-%EB%AA%A8%EB%93%A0-%EA%B2%83/