Assume there is a virus in a town, and there exists one patient on day 1. Assume that the patient transmits the virus to another person once per day, then this
other person becomes a patient, and that all carriers spread the virus at the same rate,
i. e. each patient passes the virus on to one other person per day.
Once someone has caught the virus, they do not catch it again.
The town has a fixed population of 700 000 and the borders are closed so that no one
can enter or exit the town.
How many days does it take to make everyone in the town catch the virus?
Enter your answer as the number of full days needed.