Ivan Koswara's Message Board

Currently Ivan has $10$ free hours a day. If he decides to make a message board , he has to spend $5$ minutes for every question on it. Suppose that if he has $x$ followers then there are $\left\lfloor \frac{\sqrt{x}}{5} \right\rfloor$ questions on his message board daily. He doesn't want his free time to go less than $8$ hours a day, since otherwise he doesn't have enough time for things he wants to do . If he makes a message board, how many followers can he have at most?

Note:

• One hour consists of $60$ minutes.