First Non-Repeating Character

Given a string s, your task is to find the first character that does not repeat anywhere in the string. The solution should be case-sensitive, meaning that uppercase and lowercase characters are treated differently.

If all characters in the string repeat, output an empty string.

For example, for the input "stress", the output should be "t" since 't' is the first character that appears only once. Similarly, for the input "sTreSs", the answer is "T".

The problem can be mathematically described as: find the first index i such that \( \text{count}(s[i]) = 1 \), where \( \text{count}(c) \) denotes the number of occurrences of character c in s.

inputFormat

The input consists of a single line containing the string s. The string may contain letters, digits, or special characters.

Input is read from standard input (stdin).

outputFormat

Output the first non-repeating character of the string. If there is no such character, output an empty string.

Output is printed to standard output (stdout).

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