Definition: In this task, you are given an input list A. You need to convert all the alphabets in the list with a number representing their position in the English alphabet. E.g., replace A by 1, B by 2, a by 1, b by 2, and so on.
Input: ['b', 'u', 'r', '3453', '1663', 'b', '651', 'R', 'U', 'U', 'a', 'b', '2769', 'C']

2, 21, 18, 3453, 1663, 2, 651, 18, 21, 21, 1, 2, 2769, 3