Smallest Lexicographic Permutation

Given a string s, your task is to compute its lexicographically smallest permutation such that each distinct character appears exactly once. This essentially means you need to remove duplicate letters and output all unique characters sorted in increasing order according to their ASCII values.

For example, if s = "example", the output should be "aelmpx".

Note: The input string will contain only English letters.

inputFormat

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

outputFormat

Output the lexicographically smallest permutation of s that contains each distinct character exactly once.

example

aelmpx