A group of 4 people Amit, Raghu, Neel and Nikhil, arrived in a car at a friend house. The group was forced to park around the corner due to lack of parking space. It was raining heavily and group had only one umbrella. They decided to share it. Two persons would go at a time to the friend's house and one of them would come back with the umbrella. The process would be repeated until all four people reached the friend's house. If Amit, Raghu, Neel and Nikhil take 1, 2, 5 and 10 minutes respectively at their fastest speed to go the friend's house, the minimum time required for all of them to reach the friend's house is ?