|Educational Codeforces Round 19|
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:
Petya wants to get strings s and t empty and string u lexigraphically minimal.
You should write a program that will help Petya win the game.
First line contains non-empty string s (1 ≤ |s| ≤ 105), consisting of lowercase English letters.
Print resulting string u.