1) The first and last are immediately executed. 2) If there are still 2 or more prisoners remaining, the half of the remaining prisoners with the lowest numbers (rounded up) are executed. 3) If there are still 3 or more prisoners remaining, start again from Step 1.
For example, if there were 5 prisoners to start then prisoners 1 and 5 would be executed in Step 2, and prisoners 2 and 3 would be executed in Step 3, leaving prisoner 4 alive.
Is there a strategy by which Maximus can save himself? What if Maximus also wants to save his friend Romulus?