How to Easily root the lenovo s850 phone kitkat 4.4.2 android without lose of warranty?

1. If you think that you can keep warranty after root, you should not even think of rooting. You are clearly inexperienced.

2. If you think the OS version matters, you should stay away from rooting.

3. Read read read. Don't forget to read read read the instructions or you will hard brick you device. Then there's no going back. Bricking your device because you didn't read is one of the stupidest things ever.

I tried to root my phone using towel root v.1
when i pressed the one key button to root the phone.
the phone get restarted. But until the screen comes again get restarted. It was happening several times. Then i use Hard reset to troubleshoot this problem. So now i afraid to root it again. What to do. Firstly concern it then help me please.

Please not support for root
And not support by otg

Please help
Support by otg