Tax category on sale of under construction flat - long term or short term

I entered into purchase agreement with a builder for a flat and sold it as follows

Date of Allotment letter from builder for purchase of under construction flat - 05/12/2013
Date of Agreement with builder for purchase of the under construction flat - 27/01/2014 (not registered)
Date of Possession letter from the builder - 14/07/2018
Date of agreement for CHANGE OF NOMINATION between builder, myself and new purchaser and accomplishment of  NOMINATION CHANGE- 17/09/2018

Kindly inform whether the type of gain is long term or short term.