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.
['O', '1591', 'u', 'Y', '3961', '6973', '3323', 'L', 'w', 'K', '5873', 'i', '653', 'M', '6611', 'L', 'M', 'r']