Finding a palindrome

Limits: 2 sec., 256 MiB

This statement was translated automatically from Ukrainian.

Zenyk has a string \(s\) of length \(n\), where each character is either 0 or 1. Zenyk can delete characters from the string \(s\), but exams are coming soon and little time is left, so he can delete at most half of the characters.

Marichka likes palindromes — strings that read the same from left to right and from right to left.

Help Zenyk delete at most half of the characters so that the final string pleases Marichka (i.e., is a palindrome).

Input

The first line contains a positive integer \(n\) — the length of the string.

The second line contains \(s\) — the string from which characters need to be deleted.

Output

Output the final string after deleting at most half of the characters.

Constraints

\(1 \le |s| \le 10^5\).

Samples