Idea giving rs 100 extra on Rs. 450 recharge

today i recharged my mobile for rs 450 (which gives 100 sms and 300 IDEAtoIDEA gujarat circle calls free)..by evening i had rs 100 extra in my balance..

On my previous recharge also i got rs 100 extra.. how is god so graceful on me, i have no idea..
If you are in gujarat, INDIA and an idea mobile customer, you may want to try your luck..