In this task, you are given a string of characters. You need to remove duplicate characters from the string if any, and return the resulting string.

Example Input: NmtgUlgBDHQDBjDaXxen
Example Output: NmtgUlBDHQjaXxen

Example Input: zadFNuqfDNJaQRTkfzYPDrlod
Example Output: zadFNuqfDJQRTkYPrlo

Example Input: UjLmtcNFWOcqWdjClGGYxdbR
Example Output:
UjLmtcNFWOqdClGYxbR