615. Remove Duplicate Letters

Given a string s, remove duplicate letters so that every letter appears exactly once, and return the lexicographically smallest result among all such possibilities. The input is JSON {s}.

Input: JSON {s}.

Output: String — the smallest de-duplicated string.

Examples

Input: {"s":"cbacdcbc"}
Output: acdb
Explanation: Smallest string with each letter once.

Input: {"s":"bcabc"}
Output: abc
Explanation: Each letter once, smallest order.

Input: {"s":"a"}
Output: a
Explanation: Single letter.

Constraints

• 1<=|s|<=10^4
• lowercase letters

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