First Non-Repeating Character

Given a string s, find and print the first character that does not repeat in the string. If no such character exists, print None.

In other words, if we define the count of character \(c\) in \(s\) as \(count(c)\), the task is to find the first \(c\) (in the order of appearance) for which \(count(c)=1\). If there is no character satisfying this condition, output None.

Note: The input is provided via standard input (stdin) and the output should be printed to standard output (stdout).

inputFormat

The input consists of a single line string s.

Constraints: The length of s can be assumed to be reasonably small for the context of typical coding competitions.

outputFormat

If there exists a non-repeating character, output the first non-repeating character. Otherwise, output None.

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