intertwingly

My daughter was given the following puzzle as extra credit:

Four men want to cross a bridge.  The bridge is of a width such that a maximum of 2 people may cross at a time. 

One man takes 10 minutes to cross, another takes 5 minutes to cross, another takes 2 minutes to cross, and the last takes 1 minute to cross.

Here is the catch.  If two people cross the bridge together, they must walk at the pace of the slower one. Also, it is night. Each trip requires a flashlight.  There is only one flashlight. The men are not allowed to toss the light over the river.

How fast can you get all 4 men over the bridge?

Note: try to figure it out for yourself before looking at the comments.