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: ['3291', 's', 'Q', '9399', '5505', 'C', '8879', '2435', 'U', '5875', '9217', '6139', 'l', 'L', '7145', 'B', '6063', 'D', '2831', 'z']

3291, 19, 17, 9399, 5505, 3, 8879, 2435, 21, 5875, 9217, 6139, 12, 12, 7145, 2, 6063, 4, 2831, 26