Excel Column Number Conversion

Given a column title as it appears in an Excel sheet, your task is to return its corresponding column number.

Example:

Input:

S = "AB"

Output:

28

Explanation:

The sequence is as follows:
A -> 1
B -> 2
C -> 3
...
Z -> 26
AA -> 27
AB -> 28

Constraints:

• 1 <= |S| <= 10
• S consists only of uppercase English Alphabet letters

Note:

Consider implementing the function to convert the Excel column title to a number. You do not have to handle input/output explicitly.