A group of four people needs to cross a bridge at night. The bridge is very old and rickety. They have only one torch and because it's night-time, the torch is necessary to cross the bridge. Each person walks at a different speed: - A takes 1 minute to cross, - B takes 2 minutes, - C takes 5 minutes, and - D takes 10 minutes. What is the fastest time they can all get across the bridge?