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  1. Prepare
  2. Functional Programming
  3. Recursion
  4. String Reductions

String Reductions

Given a string, , consisting of lowercase English characters (), remove all of the characters that occurred previously in the string. Formally, remove all characters, , for:

and

Input Format

A single line of input containing a string of length .

Constraints

Output Format

Print the string after removing all the characters that occurred previously.

Sample Input #00 

accabb

Sample Output #00 

acb

Sample Input #01 

abc

Sample Output #01 

abc

Sample Input #02

pprrqq

Sample Output #02 

prq

Explanation

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.

Tested by Wanbo