The Einstein riddle is not very hard, but it requires a piece of paper, so I am going to post another one that doesn't require a piece of paper, for those who are too lazy to take one.
You can still guess that one if you want.
A man was to be sentenced, and the judge told him, "You may make a statement. If it is true, I'll sentence you to four years in prison. If it is false, I'll sentence you to six years in prison." After the man made his statement, the judge decided to let him go free. What did the man say?