I have to tell you guys that honestly those riddles are dangerous for me. At least the ones that cannot be solved in a couple of minutes. The first time I tried to solve the "#1 two doors" riddle took me about 24 hours. I almost forgot to sleep and did not eat properly. I did nothing but think about the riddle. I get obsessed with these things, until I have some kind of solution. That was years ago however, and maybe I have learned from it a little and stop thinking about it after an hour or so these days. Don't know. I liked @Mr.Ghost's "4 men, two hat colors" riddle from a few months ago, and I kept at it until I had the solution. Luckily it only took me 20 minutes