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.
['p', '6399', 'j', 'u', 'c', 'Y', '8555', 'X', '5535', '789', '3491', '5427', 'e', 'Z', '6603', '2569', 'Z', 'A']