I will be taking part in a half marathon here in the UK in March 2018 and i'm looking to start training 3 months out. How would I go about either incorporating extra running training or adapting parts of certain programs to better match the training needs for a half marathon? E.g. for the basic marathon program, should I merely shorten the longer distance/timed runs? I was planning on either doing a variation of the marathon plan or the foundation program (3 month) to account for the extra running needed.