After about a year (on/off) of running (and 3 half marathons), I'm starting to accept the idea that a warm-up before my runs might be a good idea

Soo... what's your warm-up? I'd especially like to hear of routines that take as little time as possible as I will be doing it on a busy(ish) street.
Thanks in advance!
Heidi
PS. Anyone from Paris here?!