Auto Numbering!

Hi,
I want to know how can I make an Auto number generetor ?

Let me explain!

I want to have custom Invoice number format

year (last two digits) + (latest invoice number of that year +1)

samples for 2016 :

1601
1602
1603
1604
1605
16..
16105
16106
16107
...

and when the year changes! numbering should restart :

1701
1702
1703
...

So how can I do it ?

Thanks a lot