First Non-Repeating Character

In this problem, you are given a string ( s ). Your task is to find and output the first character in the string that does not repeat anywhere else. If there is no such character, output ( \text{None} ). The comparison is case-sensitive.

For example, if ( s = \texttt{aabbccde} ), the answer is ( d ) because it is the first character that occurs exactly once. If ( s ) contains only repeating characters or is empty, output ( \text{None} ).

inputFormat

The input consists of a single line containing the string ( s ). The string may be empty and can include any characters.

outputFormat

Output the first non-repeating character in the string. If every character repeats or the string is empty, output ( \text{None} ).## sample

aabbccde

d