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.
['i', 'U', 'g', 'n', 'U', '7003', '8665', '3711', '3873', 'c', 'o', 'Y', '377', '3571', '6535', 'Y', '447', '2461', 'V']