Unique String :
Difficulty Level : Easy
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Asked In :
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Given a string s that contains characters from a to z returns the smallest subsequence of s that contains all distinct characters of 's' exactly once.
Input
The first line of input contains a single string S ($$$1 \le S \le 1e5$$$)
Output
For each output print the smallest subsequence of s that doesn't contain duplicates
Example
Input
bcabc
Output
abc
