Find the First Non-Repeating Character

Given a string (s), find the first character that does not repeat anywhere in the string. If every character repeats or the string is empty, output (\text{None}).

For example, if (s = \text{'abcab'}), the first non-repeating character is (c). Pay close attention to characters with special symbols or varying cases.

inputFormat

The input consists of a single line containing the string (s).

outputFormat

Print the first non-repeating character in the string. If no such character exists, print (\text{None}).## sample

abcab

c