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: osRkjysAYNKHZYSWIEORxnZJWf
Example Output: osRkjyAYNKHZSWIEOxnJf

Example Input: ktWYQIoDdqxfApnOvFWSAhj
Example Output: ktWYQIoDdqxfApnOvFShj

Example Input: rBeRPfuOhSCAIkgalGBywtdRPxi
Example Output:
rBeRPfuOhSCAIkgalGywtdxi