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.
['w', 'i', 'Y', '7011', '999', '2551', '9493', 'j', 'F', 'a', '5165', 'f', 'K', '8475', 'C', 'd', '3407', '9253', 'U']