Remove Duplicate Characters

You are given a string \(S\) containing alphabetical characters which may include both lowercase and uppercase letters. Your task is to remove duplicate characters from \(S\) while preserving the original order of the first occurrences.

Note: The order of characters must remain the same as in the original string, and only the first occurrence of each character is retained.

Example:

Input: geeksforgeeks
Output: geksfor

In the above example, the duplicates of characters have been removed while keeping the order of first appearances.

inputFormat

Input is read from standard input. The input consists of a single line containing the string \(S\).

Constraints: \(1 \leq |S| \leq 10^5\). The string \(S\) contains alphabetical characters (both lowercase and uppercase).

outputFormat

Output the modified string after removing duplicate characters, preserving the order of their first occurrence. Write the output to standard output.

geeksforgeeks

geksfor