Puzzle - Jungle crossing

There are five people at one end of jungle and they have only one lamp. All needs to cross jungle and be at other end. Every body has different speed of crossing jungle. Five different times taken for crossing jungle from one end to other are 1, 3, 6, 8, 12 minutes. Round trip would take twice amount of time.

Lamp would last only for 30 minutes and at a time only two people can cross.
The total time taken when two people are crossing is the maximum time of them.
Lamp has to be there while crossing as it is a night time.

What should be the sequence of crossing?
Please no thowing of lamp.

1st round----1 and 3 will go and 1 will come back
1,6,8,12======3
total time=3+1=4 minutes

2nd round----8and 12 will go and 3 will come back
1,3,6====8,12
total time---4+12+3=19 minutes

3rd round --- 1 and 6 will go and 1 will come back
1,3====6,8,12
total time----19+6+1=26 minutes

4th round..1 and 3 will go and all will be right there
no one====1,3,6,8,12
total time---26+3=29 minutes

Hoping I am right.

29 sec
combinations: 1,3
12,8
6,1
1,3