CF938F.Erasing Substrings

You are given a string $s$ , initially consisting of $n$ lowercase Latin letters. After that, you perform $k$ operations with it, where . During $i$ -th operation you must erase some substring of length exactly $2^{i-1}$ from $s$ .

Print the lexicographically minimal string you may obtain after performing $k$ such operations.

The only line contains one string $s$ consisting of $n$ lowercase Latin letters ( $1<=n<=5000$ ).

Print the lexicographically minimal string you may obtain after performing $k$ operations.

Possible operations in examples:

1. adcbca adcba aba;
2. abacabadabacaba abcabadabacaba aabadabacaba aabacaba.