Problem: Petya recieved a gift of a string s with length up to 105 characters for his birthday. He took two more empty strings t and u and decided to play a game. This game has two possible moves:
- Extract the first character of s and append t with this character.
- Extract the last character of t and append u with this character.
Petya wants to get strings s and t empty and string u lexicographically minimal.
You should write a program that will help Petya win the game.
Input Format: First line contains non-empty string s (1 ≤ |s| ≤ 105), consisting of lowercase English letters.
Output Format: Print resulting string u.