Honeywell ZWStat Z-Wave K Wire

[Mpancholi]

I have Honeywell ZWStat Z-Wave thermostat. When i open the thermostat to replace with Nest Leaning thermostat, i found that K wire is not mentioned anywhere in manual. I need help to figure out which wire will go where.

Honeywell: 

RC and R have one wire directly join with each other.

One direct wire for R

One direct wire for O/B

One direct wire for C

One direct wire for K