At rush hour, three taxi buses arrived at the stop simultaneously, all following the same route, and passengers immediately boarded them. The drivers noticed that the number of people in the different buses varied and decided to transfer some passengers so that each bus would have the same number of passengers. Determine the minimum number of passengers that need to be transferred for this. \InputFile Three integers, not exceeding $100$ --- the number of passengers in the first, second, and third busses, respectively. \OutputFile Print a single number --- the minimum number of passengers that need to be transferred. If this is impossible, print \textbf{IMPOSSIBLE}.