Given a string columnTitle that represents the column title as appears in an Excel sheet, return its corresponding column number.

• A → 1, B → 2, ..., Z → 26
• AA → 27, AB → 28, ...

Example 1:

Input: columnTitle = "AB"
Output: 28

Example 2:

Input: columnTitle = "ZY"
Output: 701

Constraints:

• 1 <= columnTitle.length <= 7