Update field name with same value as auto-number field

Update field name with same value as auto-number field

Hello,

Thanks in advanced for your help.

In DEALS module, I have two fields. 

Nº Oportunidad (autonumber field) --> generates a number when deal is created
Nombre de Oportunidad (single line mandatory field) --> is actually the name of the deal.

I need a function that updates automatically "Nombre de Oportunidad" with the same autonumber Nº Oportunidad once is created.

Thank you