How to shift down a square wave at 0 - 5 V?

How to shift down a square wave at 0 - 5 V?

I have a square wave that oscillates at 500 Hz from 12 to 14 V. I would like it to oscillate at the same frequency from 0 to 5 V, so I could use to trigger i.e. a switch. Is there any circuit to do ...