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I think it is not abnormal number of times you do in a week. But if it seems to bother you, you may try ways to distract yourself. Whenever you get such thoughts, you must immediately change your mind to something else you like to do and then do that only, like any hobbies, watching movies, talking to friends. Try it slowly. If this doesn't work, you may contact a Psychiatrist
to help you in dealing with this problem.