autogenerated number in a format

Question

hello.

i've a table in which country code and city code exists. there is a hotel code field as well.

i wants to generate autonumber including country and city code.

for example:-

"IND-DEL-0001" 

1ST PART IS COUNTRY CODE 2ND PART IS CITY CODE. 3RD PART IS AUTOGENERATED AND STARTING FROM "0001".

please suggest code to achieve this.

thank you.