In this task, you are given an input list A. You need to find all the elements of the list that are numbers and calculate their sum.
['K', 'O', '9547', 'Y', '4517', '9297', '631', '6977', '1193', '3455', '8771', 'c', '945', 'Q', 'U', '9111', 'q', '6391', '4023', 'S']