Description: 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. Note: None