The following section describes how to establish the code to a locked door in block B of the asylum in Get Even. You will have to solve this puzzle during your second visit in block B of the Asylum, while playing as Black. This takes place after you complete "Job for Robert Ramsey". The puzzle is related to one of the patients - John Keating.
When exploring block B of the asylum, you will pass by John Keating's cell and reach the locked door presented in the screenshot. Investigate it and you will learn that you will need a four digit code to unlock it.
Get back to Keating's cell and listen to a short conversation with him - this is your hint. You need to check cells from the previous corridor and look for digits that are part of the code.
Start with the cell close to the location where you began exploring this part of the asylum. Use the UV lamp to light the wall and reveal one of the digits - in our case it was 1.
Go to the next cell and use the UV lamp again. Do the math - in our case it was 4+4=8.
Visit the next cell. You will have to add all the numbers from the marked area - in our case it was 1+2+1+0=4.
Search the last cell. Once again you will have to do some basic math. Just add the winning numbers of tic-tac-toe - in our case it was 2+2+1=5.
Get back to the locked gate and type in the code. Our combination was 1845 but it is possible that due to a random scenario you may have to use a different code (based on the digits on the walls).