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.
['s', 'h', '2569', '3565', 'c', 'v', 'f', '6399', '3843', '6217', 'Q', 'n', '1297', 'u', '5051', 'L', '3331', 'K']