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: ['p', 'A', '5129', 's', 'b', '153', '5499', 'U']

16, 1, 5129, 19, 2, 153, 5499, 21