Unique Non-Repeating Characters

Given a string of alphanumeric characters, your task is to generate a new string that consists only of the characters that appear exactly once in the original string. The order of characters must be maintained as in the original string.

For example:

• If the input is abcde, then the output should be abcde because all characters are unique.
• If the input is swiss, then the output should be wi because 's' is repeated.
• If the input is aabbcc, then the output should be an empty string since every character appears more than once.
• If the input is an empty string, the output should also be an empty string.
• Case is significant, so for aAbBcCdD the result is aAbBcCdD.
• For numerical strings like 123324, the answer is 14, since digits '2' and '3' are repeated.
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Note: The solution should work for any string containing alphanumeric characters. In mathematical notation, if S is the set of characters in the string with frequency function \( f: S \to \mathbb{N} \), then the result is R = { c \in S : f(c)=1 } keeping the order of appearance.

inputFormat

The input consists of a single line that contains a string s composed of alphanumeric characters.

outputFormat

Output the new string that contains only the characters that occur exactly once in s, in the order of their first appearance.

## sample

abcde

abcde