Bridge Crossing

There are four people who want to cross a bridge. They take 1, 2, 5 and 10 minutes, respectively. They're crossing at night, so, to cross, you need a lantern, and they have one between the four of them. The bridge is only wide enough to fit two people crossing at a time.

What's the floor on their crossing time? That is, what's the shortest possible time for them all to cross?