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.
['d', 'P', 'Z', '5335', 'O', 'v', '3639', '7367', '2957', '2457', 'W', 'p', '2979', '4689', '1291', '3683', 'K', '1399']