You are given a string, str, of length N consisting of lowercase letters of alphabet. You have to remove all those characters from str which have already appeared in it, i.e., you have to keep only first occurance of each letter.

Input Format
First line of input contains a string str of length N.

Output Format
A string with removed characters as described in the problem.

Constraints
1 <= N <= 30000
str will contain only lowercase letters ('a'-'z').

Sample Input #00

aabc

Sample Output #00

abc

Sample Input #01

ccbabacc

Sample Output #01

cba

Explanation
Test Case #00: Here you have to remove 'a' at index 1 (0 based indexing) because it has already appeared at index 0.
Test Case #01: Here you have to remove 'c' from index 1, 6 and 7, because 'c' has already appeared at index 0. Similarly you have to remove 'b' from index 4 and 'a' from index 5.

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Tested by: Tusshar Singh, Abhiranjan Kumar