Remove Duplicate Characters

You are given a string s consisting of lowercase letters. Your task is to remove duplicate characters from the string while maintaining the order of their first occurrence.

For example, if s = "programming", then the output should be "progamin" because the first occurrence of each character is preserved and duplicates are removed.

This is a typical problem that tests your ability to process strings and use data structures to track seen characters.

Input constraints: The input string may be empty or contain up to 10⁵ characters.

inputFormat

The input is read from standard input (stdin). It consists of a single line containing a string s of lowercase letters.

outputFormat

The output should be printed to standard output (stdout) as a single line string after removing duplicate characters while maintaining the order of their first occurrence.

programming

progamin