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.
['4997', '5005', '6773', 'q', 'K', '8391', '7303', 'K', 'N', '5417', '8573', 'z', '8653', '8343', 'm', 'L', '1587', 'p', '5323']