I am appearing for the May 13 exams. Presently I am working in a company and cant affort to attend any class because of my office hours. So, I was kind of thinking to buy DVDs of lectures given by eminent teachers. Are the DVDs on SFM by Dr. J.B. Gupta reliable? I mean, hw much time will it take to learn the subject by following his book and DVDs? I would like to purchase it if it is a viable option.