First Non-Repeating Character

Given a string s, your task is to find and return the first character that does not repeat anywhere in the string. If every character appears at least twice, print All characters are repeating.

Note that the search is case-sensitive, i.e., 'a' and 'A' are considered different characters.

The algorithm follows these steps:

• Count the occurrence of each character in the string.
• Iterate over the string to find the first character with count equal to 1.
• If no such character exists, output the message "All characters are repeating".

The frequency, f, of each character x in the string can be expressed as \( f(x) \). We need to find the first \( x \) such that \( f(x) = 1 \).

inputFormat

The input consists of a single line containing the string s. The string may be empty.

outputFormat

Output a single line with the first non-repeating character. If every character repeats, output All characters are repeating.

aabc

b