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', 'n', 's', 'v', '473', '3817', '411', 'd', '3139', '1997', 'I', 'E', '2621', '2019', 'D', 'p', '3899', '539']

2, 14, 19, 22, 473, 3817, 411, 4, 3139, 1997, 9, 5, 2621, 2019, 4, 16, 3899, 539