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

For example:

A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 ...

  Example 1:

Input: columnTitle = "A" Output: 1

Example 2:

Input: columnTitle = "AB" Output: 28

Example 3:

Input: columnTitle = "ZY" Output: 701

  Constraints:

1 <= columnTitle.length <= 7
columnTitle consists only of uppercase English letters.
columnTitle is in the range ["A", "FXSHRXW"].