Ashok, Balu, Chiru, and Dareesh are crossing a bridge at night which requires a torch light. With a given torch maximum only 2 people can walk together. If third person tries to walk with them, then one of them may fall into the water. Each of them crosses the bridge with different speeds. Ashok takes one minute, Balu takes 2 minutes, Chiru takes seven minutes, and Dareesh takes ten minutes to cross.
Find out what is the shortest time for all of them to cross that bridge?
Note: If two persons are walking together, then faster person has to slow down to accompany the slower rate person.