Sorry, but I totally disagree with @Jett. A first employee or early employee is NOT a co-founder. Co-founders must share an identical vision for the company, are a decision-maker for the business, and have an inherent ownership. Employees are not required to have any of those things.
The answer is most likely zero. Anyone coming in that early is a cofounder, not an employee. Unless you are paying someone a market rate salary of course. Then we'd need a bit more info to be able to answer that question.