First Non-Repeating Alphabetical Character

Given a string s, your task is to find and return the first alphabetical character that does not repeat. Only alphabetical characters (a-z and A-Z) are considered, and uppercase and lowercase letters are treated as distinct. If every alphabetical character in the string repeats at least once, output None.

Input will be provided via standard input and the result should be printed to standard output.

inputFormat

A single line string s.

outputFormat

Print the first non-repeating alphabetical character. If no such character exists, print None.## sample

swiss

w