What should be the minimum sleeping hours of a workaholic adult male?

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Sleeping is must for a human being, it is the time when your brain get some relaxation after a full day of work or schedule. If our brain doesn't get the minimum time of relaxation then many disorders may happen. So from my point of view 8 hours of sleep is mandatory for every adult. But the persons who are workaholic does want to give that much of time in sleeping. What should be an ideal or minimum sleeping hours for such workaholic persons.