Once upon a time, there was a king, who found out that his wife, the queen, had an affair with Tristan, one of his knights. He gets mad and calls all his knights and Tristan: "I found out that you have a relationship with the queen, Tristan. Tomorrow morning, I will give you a bag with 3 white stones and 1 red stone. If you pick out the red stone, you are a free man. But if you pick out a white stone, you will be executed." In the evening, the king prepares the bag with the stones. But he wants to get sure that Tristan picks out a white stone, so he puts in 4 white stones and 1 red stone to increase the probability of picking out a white stone. The queen notices that and during the night she tells Tristan what she saw. The next morning, Tristan is called to come to the king and his knights. The king gives him the bag. How does Tristan survive?