This is my personal opinion and please feel free to differ, but I really feel Kolkata weather is not at all conducive to the heavily coated breeds like the Tibetan Mastiff or St. Bernard. While they might survive, they feel definitely be extremely uncomfortable in the long summer and mild winter of Kolkata. While an AC might help, it is hardly possible to always keep the dog in an AC environment. Even exercising it will become tough. And the high humidity of Kolkata makes air coolers absolutely useless in Kolkata. Might be a much better idea to find a breed better suited to the climate. All the best!