GT-I9300 accidentally deleted OS

[AC Question]

Hi guys, when I want to install custom ROM to my phone Samsung Galaxy S3 (GT-I9300), I was in the TWRP Recovery mode, but I accidentally deleted my OS. My phone is not function now, TWRP also keep bootloop. Tried to connect to Odin but not detected. I really want to save my phone. This is my only phone, I hope there's someone can help me solve this problem. Thanks!