The host has ten locked boxes. Half of them contain rocks, and the other half contain gems. The host knows what is inside in each of the boxes. You are asked to randomly select one box (without opening it). After you select a box, the host opens a box which contains a rock from the rest nine boxes and shows you. Then, the host asks you whether to switch to another unopened box. In order to maximize the chance of winning a gem, should you switch, or not switch, or it does not make any difference? The decision is ________________________________