There are $30$ cities in the empire of Euleria. Every week, Martingale City runs a very well-known lottery. $900$ visitors decide to take a trip around the empire, visiting a different city each week in some random order. $3$ of these cities are inhabited by mathematicians, who will talk to all visitors about the laws of statistics. A visitor with this knowledge has a probability of $0$ of buying a lottery ticket, else they have a probability of $0.5$ of buying one. What is the expected number of visitors who will play the Martingale Lottery?

Let's think step by step and output the final answer within \boxed{}.
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