Given a string, , consisting of lowercase English characters (), remove all of the characters that occurred previously in the string. Formally, remove all characters, , for:
A single line of input containing a string of length .
Print the string after removing all the characters that occurred previously.
Sample Input #00
Sample Output #00
Sample Input #01
Sample Output #01
Sample Input #02
Sample Output #02
Test case #00: For , characters at indexes are removed as they have already occurred. Test case #01: As each character occurs only once, nothing is removed. Test case #02: For , each character occurs twice. The second of these characters is removed. Characters at positions and are removed.